Antiviral CD4 and CD8 T–cell memory: differences in the size of the response and activation requirements

Following acute lymphocytic choriomeningitis virus (LCMV) infection, there is a potent antiviral CD8 T–cell response that eliminates the infection. This initial CD8 T–cell response is followed by a period of memory during which elevated numbers of virus–specific CD8 T cells remain in the mouse. CD4 T cells are also activated after LCMV infection, but relatively less is known about the magnitude and duration of the CD4 response. In this study, we used intracellular staining for interferon–γ to measure both CD4 and CD8 responses in the same mice at the single cell level. After LCMV infection, there was an increase in the number of activated CD4 T cells and an associated increase in the number of virus–specific CD4 T cells. At the peak of this expansion phase, the frequency of virus–specific CD4 T cells was 1 in 20 (0.5–1.0 × 106 per spleen). Like the CD8 response, long–term CD4 memory could be found up to a year after the infection with frequencies of approximately 1 in 260 (0.5–1.5 × 105 per spleen). However, the magnitude of virus–specific CD8 T cells was greater than virus–specific CD4 T cells during all phases of the immune response (expansion, death, and memory). At day 8, there were 20– to 35–fold more virusspecific CD8 Tcells than CD4 Tcells. This initial difference in cell number lasted into the memory phase as there remained a ten– to 20–fold difference in the CD8 and CD4 responses. These results highlight the importance of the expansion phase in determining the size of the memory T–cell pool. In addition to the difference in the magnitude, the activation requirements of CD8 and CD4 T–cell responses were different: CD8 T responses were not affected by blockade of CD40– CD40 ligand interaction whereas CD4 responses were reduced 90%. So while there is long–term memory in both the CD8 and CD4 compartments, the rules regulating the activation of CD8 and CD4 T cells and the overall magnitude of the responses are different.

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Role of Thymic Output in Regulating CD8 T-Cell Homeostasis during Acute and Chronic Viral Infection

Journal of Virology ◽

10.1128/jvi.79.15.9419-9429.2005 ◽

2005 ◽

Vol 79 (15) ◽

pp. 9419-9429 ◽

Cited By ~ 29

Author(s):

Nicole E. Miller ◽

Jennifer R. Bonczyk ◽

Yumi Nakayama ◽

M. Suresh

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Cell Response ◽

Viral Infections ◽

T Cell Responses ◽

Cd8 T Cell ◽

T Cell Response ◽

Cell Responses ◽

Lcmv Infection

ABSTRACT Although it is well documented that CD8 T cells play a critical role in controlling chronic viral infections, the mechanisms underlying the regulation of CD8 T-cell responses are not well understood. Using the mouse model of an acute and chronic lymphocytic choriomeningitis virus (LCMV) infection, we have examined the relative importance of peripheral T cells and thymic emigrants in the elicitation and maintenance of CD8 T-cell responses. Virus-specific CD8 T-cell responses were compared between mice that were either sham thymectomized or thymectomized (Thx) at ∼6 weeks of age. In an acute LCMV infection, thymic deficiency did not affect either the primary expansion of CD8 T cells or the proliferative renewal and maintenance of virus-specific lymphoid and nonlymphoid memory CD8 T cells. Following a chronic LCMV infection, in Thx mice, although the initial expansion of CD8 T cells was normal, the contraction phase of the CD8 T-cell response was exaggerated, which led to a transient but striking CD8 T-cell deficit on day 30 postinfection. However, the virus-specific CD8 T-cell response in Thx mice rebounded quickly and was maintained at normal levels thereafter, which indicated that the peripheral T-cell repertoire is quite robust and capable of sustaining an effective CD8 T-cell response in the absence of thymic output during a chronic LCMV infection. Taken together, these findings should further our understanding of the regulation of CD8 T-cell homeostasis in acute and chronic viral infections and might have implications in the development of immunotherapy.

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Antigen persistence is required throughout the expansion phase of a CD4+ T cell response

Journal of Experimental Medicine ◽

10.1084/jem.20042521 ◽

2005 ◽

Vol 201 (10) ◽

pp. 1555-1565 ◽

Cited By ~ 190

Author(s):

Reinhard Obst ◽

Hisse-Martien van Santen ◽

Diane Mathis ◽

Christophe Benoist

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Cell Response ◽

Cd4 T Cells ◽

T Cell Response ◽

T Cell Subsets ◽

Cd4 T Cell ◽

Expansion Phase ◽

Antigen Persistence

For CD8+ T cells, a relatively short antigen pulse seems sufficient for antigen-presenting cells to drive clonal expansion and differentiation. It is unknown whether the requirement for antigen is similarly ephemeral for CD4+ T cells. To study the dependence of a CD4+ T cell response on antigen persistence in a quantitatively and temporally controlled manner in vivo, we engineered a mouse line expressing a major histocompatibility complex class II–restricted epitope in dendritic cells under the control of a tetracycline-inducible promoter. Experiments tracking the proliferation of CD4+ T cells exposed to their cognate antigen in various amounts for different time periods revealed that the division of such cells was contingent on the presence of antigen throughout their expansion phase, even in the presence of an inflammatory stimulus. This previously unrecognized feature of a CD4+ T cell response contrasts with the proliferative behavior of CD8+ T cells that has been documented, and it implies that the two T cell subsets might require different strategies for efficient vaccination.

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Type I Interferons Regulate the Magnitude and Functionality of Mouse Polyomavirus-Specific CD8 T Cells in a Virus Strain-Dependent Manner

Journal of Virology ◽

10.1128/jvi.00199-16 ◽

2016 ◽

Vol 90 (10) ◽

pp. 5187-5199 ◽

Cited By ~ 7

Author(s):

Qingsong Qin ◽

Shwetank ◽

Elizabeth L. Frost ◽

Saumya Maru ◽

Aron E. Lukacher

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Cell Response ◽

Cd8 T Cell ◽

T Cell Response ◽

Single Amino Acid ◽

Type I ◽

Type I Ifns ◽

Vp1 Capsid Protein

ABSTRACTMouse polyomavirus (MPyV) is a ubiquitous persistent natural mouse pathogen. A glutamic acid (E)-to-glycine (G) difference at position 91 of the VP1 capsid protein shifts the profile of tumors induced by MPyV from an epithelial to a mesenchymal cell origin. Here we asked if this tropism difference affects the MPyV-specific CD8 T cell response, which controls MPyV infection and tumorigenesis. Infection by the laboratory MPyV strain RA (VP1-91G) or a strain A2 mutant with an E-to-G substitution at VP1 residue 91 [A2(91G)] generated a markedly smaller virus-specific CD8 T cell response than that induced by A2(VP1-91E) infection. Mutant A2(91G)-infected mice showed a higher frequency of memory precursor (CD127hiKLRG1lo) CD8 T cells and a higher recall response than those of A2-infected mice. Using T cell receptor (TCR)-transgenic CD8 T cells and immunization with peptide-pulsed dendritic cells, we found that early bystander inflammation associated with A2 infection contributed to recruitment of the larger MPyV-specific CD8 T cell response. Beta interferon (IFN-β) transcripts were induced early during A2 or A2(91G) infections. IFN-β inhibited replication of A2 and A2(91G)in vitro. Using mice lacking IFN-αβ receptors (IFNAR−/−), we showed that type I IFNs played a role in controlling MPyV replicationin vivobut differentially affected the magnitude and functionality of virus-specific CD8 T cells recruited by A2 and A2(91G) viral infections. These data indicate that type I IFNs are involved in protection against MPyV infection and that their effect on the antiviral CD8 T cell response depends on capsid-mediated tropism properties of the MPyV strain.IMPORTANCEIsolates of the human polyomavirus JC virus from patients with the frequently fatal demyelinating brain disease progressive multifocal leukoencephalopathy (PML) carry single amino acid substitutions in the domain of the VP1 capsid protein that binds the sialic acid moiety of glycoprotein/glycolipid receptors on host cells. These VP1 mutations may alter neural cell tropism or enable escape from neutralizing antibodies. Changes in host cell tropism can affect recruitment of virus-specific CD8 T cells. Using mouse polyomavirus, we demonstrate that a single amino acid difference in VP1 known to shift viral tropism profoundly affects the quantity and quality of the anti-polyomavirus CD8 T cell response and its differentiation into memory cells. These findings raise the possibility that CD8 T cell responses to infections by human polyomaviruses may be influenced by VP1 mutations involving domains that engage host cell receptors.

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MOG extracellular domain (p1–125) triggers elevated frequency of CXCR3+ CD4+ Th1 cells in the CNS of mice and induces greater incidence of severe EAE

Multiple Sclerosis Journal ◽

10.1177/1352458514524086 ◽

2014 ◽

Vol 20 (10) ◽

pp. 1312-1321 ◽

Cited By ~ 5

Author(s):

Jyothi T Mony ◽

Reza Khorooshi ◽

Trevor Owens

Keyword(s):

T Cells ◽

T Cell ◽

Cell Response ◽

Cd4 T Cells ◽

Cd8 T Cell ◽

Interferon Γ ◽

T Cell Response ◽

Receptor Expression ◽

Myelin Proteins ◽

Mhc Ii

Background: Myelin-specific T cells are implicated in multiple sclerosis (MS) and drive experimental autoimmune encephalomyelitis (EAE). EAE is commonly induced with short peptides, whereas in MS, whole myelin proteins are available for immune response. We asked whether immunization with the immunoglobulin-like domain of myelin oligodendrocyte glycoprotein (MOGIgd, residues 1–125) might induce distinct CD4+ T-cell response and/or a stronger CD8+ T-cell response, compared to the 21 amino acid immunodominant MHC II-associating peptide (p35–55). Objectives: Compare both EAE and T-cell responses in C57BL/6 mice immunized with MOGIgd and MOG p35–55. Methods: Cytokine production, and chemokine receptor expression by CD4+ and CD8+ T cells in the mouse central nervous system (CNS), were analyzed by flow cytometry. Results: MOGIgd triggered progression to more severe EAE than MOG p35–55, despite similar time of onset and overall incidence. EAE in MOGIgd-immunized mice was characterized by an increased percentage of CXCR3+ interferon-γ-producing CD4+ T cells in CNS. The CD8+ T-cell response to both immunogens was similar. Conclusions: Increased incidence of severe disease following MOGIgd immunization, accompanied by an increased percentage of CD4+ T cells in the CNS expressing CXCR3 and producing interferon-γ, identifies a pathogenic role for interferon-γ that is not seen when disease is induced with a single Major Histocompatibility Complex (MHC) II-associating epitope.

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Mucosal CD8+ T cell responses induced by an MCMV based vaccine vector confer protection against influenza challenge

10.1101/494864 ◽

2018 ◽

Author(s):

Xiaoyan Zheng ◽

Jennifer Dora Oduro ◽

Julia Désirée Boehme ◽

Lisa Borkner ◽

Thomas Ebensen ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Cell Response ◽

Influenza A ◽

Clinical Medicine ◽

Cd8 T Cell ◽

T Cell Response ◽

Vaccine Vector ◽

Protective Capacity

Cytomegalovirus (CMV) is a ubiquitous β-herpesvirus that establishes life-long latent infection in a high percentage of the population worldwide. CMV induces the strongest and most durable CD8+ T cell response known in human clinical medicine. Due to its unique properties, the virus represents a promising candidate vaccine vector for the induction of persistent cellular immunity. To take advantage of this, we constructed a recombinant murine CMV (MCMV) expressing an MHC-I restricted epitope from influenza A virus (IAV) H1N1 within the immediate early 2 (ie2) gene. Only mice that were immunized intranasally (i.n.) were capable of controlling IAV infection, despite the greater potency of the intraperitoneally (i.p.) vaccination in inducing a systemic IAV-specific CD8+ T cell response. The protective capacity of the i.n. immunization was associated with its ability to induce IAV-specific tissue-resident memory CD8+ T (CD8TRM) cells in the lungs. Our data demonstrate that the protective effect exerted by the i.n. immunization was critically mediated by antigen-specific CD8+ T cells. CD8TRM cells promoted the induction of IFNγ and chemokines that facilitate the recruitment of antigen-specific CD8+ T cells to the lungs. Overall, our results showed that locally applied MCMV vectors could induce mucosal immunity at sites of entry, providing superior immune protection against respiratory infections.

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Chimeric Yellow Fever/Dengue Virus as a Candidate Dengue Vaccine: Quantitation of the Dengue Virus-Specific CD8 T-Cell Response

Journal of Virology ◽

10.1128/jvi.74.17.8094-8101.2000 ◽

2000 ◽

Vol 74 (17) ◽

pp. 8094-8101 ◽

Cited By ~ 77

Author(s):

Robbert G. van der Most ◽

Kaja Murali-Krishna ◽

Rafi Ahmed ◽

James H. Strauss

Keyword(s):

T Cells ◽

T Cell ◽

Dengue Virus ◽

Yellow Fever ◽

Cd8 T Cells ◽

Cell Response ◽

Protective Efficacy ◽

Cd8 T Cell ◽

T Cell Response ◽

E Proteins

ABSTRACT We have constructed a chimeric yellow fever/dengue (YF/DEN) virus, which expresses the premembrane (prM) and envelope (E) genes from DEN type 2 (DEN-2) virus in a YF virus (YFV-17D) genetic background. Immunization of BALB/c mice with this chimeric virus induced a CD8 T-cell response specific for the DEN-2 virus prM and E proteins. This response protected YF/DEN virus-immunized mice against lethal dengue encephalitis. Control mice immunized with the parental YFV-17D were not protected against DEN-2 virus challenge, indicating that protection was mediated by the DEN-2 virus prM- and E-specific immune responses. YF/DEN vaccine-primed CD8 T cells expanded and were efficiently recruited into the central nervous systems of DEN-2 virus challenged mice. At 5 days after challenge, 3 to 4% of CD8 T cells in the spleen were specific for the prM and E proteins, and 34% of CD8 T cells in the central nervous system recognized these proteins. Depletion of either CD4 or CD8 T cells, or both, strongly reduced the protective efficacy of the YF/DEN virus, stressing the key role of the antiviral T-cell response.

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T Cell Recognition of HCMV: Pan-Genome Analysis of Immunogenic Open-Reading Frames.

Blood ◽

10.1182/blood.v104.11.606.606 ◽

2004 ◽

Vol 104 (11) ◽

pp. 606-606 ◽

Cited By ~ 1

Author(s):

Louis J. Picker ◽

Andrew W. Sylwester ◽

Bridget L. Mitchell ◽

Cara Taormina ◽

Christian Pelte ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Peripheral Blood ◽

Cell Response ◽

Cd8 T Cell ◽

Cross Reactivity ◽

T Cell Response ◽

Cd4 T Cell ◽

Cell Responses

Abstract Human Cytomegalovirus (HCMV) is among the largest and most complex of known viruses with 150–200nm virions enclosing a double stranded 230kb DNA genome capable of coding for >200 proteins. HCMV infection is life-long, and for the vast majority of immune competent individuals clinically benign. Disease occurs almost exclusively in the setting of immune deficiency, suggesting that the stable host-parasite relationship that characterizes these infections is the result of an evolutionarily “negotiated” balance between viral mechanisms of pathogenesis and the host immune response. In keeping with, and perhaps because of this balance, the human CD4+ T cell response to whole HCMV viral lysates is enormous, with median peripheral blood frequencies of HCMV-specific cells ~5–10 fold higher than for analogous preparations of other common viruses. Although certain HCMV ORFs have been identified as targets of either the CD4+ or CD8+ T cell response, the specificities comprising the CD4+ T cell response, and both the total frequencies and component parts of the CD8+ T cell response are unknown. Here, we used cytokine flow cytometry and ~14,000 overlapping 15mer peptides comprising all 213 HCMV ORFs encoding proteins >100 amino acids in length to precisely define the total CD4+ and CD8+ HCMV-specific T cell responses and the HCMV ORFs responsible for these responses in 33 HCMV-seropositive, HLA-disparate donors. An additional 9 HCMV seronegative donors were similarly examined to define the extent to which non-HCMV responses cross-react with HCMV-encoded epitopes. We found that when totaled, the median frequencies of HCMV-specific CD4+ and CD8+ T cells in the peripheral blood of the seropositive subjects were 4.0% and 4.5% for the total CD4+ or CD8+ T cell populations, respectively (which corresponds to 9.1% and 10.5% of the memory populations, respectively). The HCMV-specific CD4+ and CD8+ T cell responses included a median 12 and 7 different ORFs, respectively, and all told, 73 HCMV ORFs were identified as targets for both CD4+ and CD8+ T cells, 26 ORFs as targets for CD8+ T cells alone, and 43 ORFS as targets for CD4+ T cells alone. UL55, UL83, UL86, UL99, and UL122 were the HCMV ORFs most commonly recognized by CD4+ T cells; UL123, UL83, UL48, UL122 and UL28 were the HCMV ORFs most commonly recognized by CD8+ T cells. The relationship between immunogenicity and 1) HLA haplotype and 2) ORF expression and function will be discussed. HCMV-seronegative individuals were non-reactive with the vast majority of HCMV peptides. Only 7 potentially cross-reactive responses were identified (all by CD8+ T cells) to 3 ORFs (US32, US29 and UL116) out of a total of almost 4,000 potential responses, suggesting fortuitous cross-reactivity with HCMV epitopes is uncommon. These data provide the first glimpse of the total human T cell response to a complex infectious agent, and will provide insight into the rules governing immunodominance and cross-reactivity in complex viral infections of humans.

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The Response to Repeated Vaccination with PR1 and WT1 Peptides Admixed in Montanide Adjuvant Is Transient and Fails to Induce Sustained Anti-Leukemia Responses in Patients with Myeloid Malignancies.

Blood ◽

10.1182/blood.v114.22.4096.4096 ◽

2009 ◽

Vol 114 (22) ◽

pp. 4096-4096

Author(s):

Katayoun Rezvani ◽

Agnes S. M. Yong ◽

Stephan Mielke ◽

Behnam Jafarpour ◽

Bipin N. Savani ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Cell Response ◽

T Cell Responses ◽

Cd8 T Cell ◽

T Cell Response ◽

Gm Csf ◽

Cell Responses ◽

Ifn Γ

Abstract Abstract 4096 Poster Board III-1031 We previously demonstrated the immunogenicity of a combined vaccine approach employing two leukemia-associated antigenic peptides, PR1 and WT1 (Rezvani Blood 2008). Eight patients with myeloid malignancies received one subcutaneous 0.3 mg and 0.5 mg dose each of PR1 and WT1 vaccines in Montanide adjuvant, with 100 μg of granulocyte-macrophage colony-stimulating factor (GM-CSF). CD8+ T-cell responses against PR1 or WT1 were detected in all patients as early as 1 week post-vaccination. However, responses were only sustained for 3-4 weeks. The emergence of PR1 or WT1-specific CD8+ T-cells was associated with a significant but transient reduction in minimal residual disease (MRD) as assessed by WT1 expression, suggesting a vaccine-induced anti-leukemia response. Conversely, loss of response was associated with reappearance of WT1 transcripts. We hypothesized that maintenance of sustained or at least repetitive responses may require frequent boost injections. We therefore initiated a phase 2 study of repeated vaccination with PR1 and WT1 peptides in patients with myeloid malignancies. Five patients with acute myeloid leukemia (AML) and 2 patients with myelodysplastic syndrome (MDS) were recruited to receive 6 injections at 2 week intervals of PR1 and WT1 in Montanide adjuvant, with GM-CSF as previously described. Six of 7 patients completed 6 courses of vaccination and follow-up as per protocol, to monitor toxicity and immunological responses. Responses to PR1 or WT1 vaccine were detected in all patients after only 1 dose of vaccine. However, additional boosting did not further increase the frequency of PR1 or WT1-specific CD8+ T-cell response. In 4/6 patients the vaccine-induced T-cell response was lost after the fourth dose and in all patients after the sixth dose of vaccine. To determine the functional avidity of the vaccine-induced CD8+ T-cell response, the response of CD8+ T-cells to stimulation with 2 concentrations of PR1 and WT1 peptides (0.1 and 10 μM) was measured by IC-IFN-γ staining. Vaccination led to preferential expansion of low avidity PR1 and WT1 specific CD8+ T-cell responses. Three patients (patients 4, 6 and 7) returned 3 months following the 6th dose of PR1 and WT1 peptide injections to receive a booster vaccine. Prior to vaccination we could not detect the presence of PR1 and WT1 specific CD8+ T-cells by direct ex-vivo tetramer and IC-IFN-γ assay or with 1-week cultured IFN-γ ELISPOT assay, suggesting that vaccination with PR1 and WT1 peptides in Montanide adjuvant does not induce memory CD8+ T-cell responses. This observation is in keeping with recent work in a murine model where the injection of minimal MHC class I binding peptides derived from self-antigens mixed with IFA adjuvant resulted in a transient effector CD8+ T cell response with subsequent deletion of these T cells and failure to induce CD8+ T cell memory (Bijker J Immunol 2007). This observation can be partly explained by the slow release of vaccine peptides from the IFA depot without systemic danger signals, leading to presentation of antigen in non-inflammatory lymph nodes by non-professional antigen presenting cells (APCs). An alternative explanation for the transient vaccine-induced immune response may be the lack of CD4+ T cell help. In summary these data support the immunogenicity of PR1 and WT1 peptide vaccines. However new approaches will be needed to induce long-term memory responses against leukemia antigens. To avoid tolerance induction we plan to eliminate Montanide adjuvant and use GM-CSF alone. Supported by observations that the in vivo survival of CD8+ T-effector cells against viral antigens are improved by CD4+ helper cells, we are currently attempting to induce long-lasting CD8+ T-cell responses to antigen by inducing CD8+ and CD4+ T-cell responses against class I and II epitopes of WT1 and PR1. Disclosures: No relevant conflicts of interest to declare.

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Recovery of CMV-Specific T Cells Following Alternative Donor Allogeneic Transplant with Post-Transplant Cyclophosphamide

Blood ◽

10.1182/blood.v126.23.5462.5462 ◽

2015 ◽

Vol 126 (23) ◽

pp. 5462-5462

Author(s):

Ayman Saad ◽

Samantha B Langford ◽

Shin Mineishi ◽

Lawrence S. Lamb

Keyword(s):

T Cells ◽

T Cell ◽

Cd8 T Cells ◽

Cell Response ◽

Cd8 T Cell ◽

T Cell Response ◽

Cell Recovery ◽

Post Transplant ◽

Increased Risk ◽

Cmv Reactivation

Abstract Background: Post-transplant cyclophosphamide (PTCy) is increasingly used for GVHD prophylaxis after allogeneic hematopoietic stem cell transplantation (HCT) using alternative donors. However, immune reconstitution can be delayed posing an increased risk for CMV reactivation. We evaluated the outcomes of patients who received HCT-apheresis products comparing the impact of PTCy on lymphocyte recovery, CMV reactivation and CMV-specific CD8+ T cell recovery following haplo-identical (HAPLO), matched unrelated donor (MUD), and mismatched unrelated donor (mMUD) grafts vs. with conventional matched related donor (MRD) graft recipients. Methods: We examined 26 patients (median age, 49 years; range, 20-72 years) with advanced hematologic malignancies; n=5 (HAPLO); 6 (MRD); 15 (MUD). All patients received myeloablative conditioning regimens that was either busulfan- or total body irradiation (TBI)-based. PTCy (50 mg/kg/day) was administered on days +3 and +4 following HAPLO and on day +3 following MUD/mMUD transplant. Peripheral blood lymphocyte reconstitution and frequency of circulating CMV-directed CD8+ T cells was assessed (day ± 10 days) on post-transplant days +30, +60, and +90. Circulating anti-CMV T cell frequency was assessed using a phycoerythrin-tagged MHC dextramer against HLA-specific CMV pp65, IE-1, or pp50 peptides (Immudex; Copenhagen, DK) in combination with Tru-Count¨ tubes and fluorescent-labeled monoclonal antibodies against CD3, CD8, CD4, CD16/56, and CD19 (BD Biosciences; San Jose, CA). Anti-CMV CD8+ T cell immunity was defined as a CMV-dextramer (CMV/DEX) positive count of ≥7cells/ml. CMV reactivation was defined as a serologic titer of >500IU/mL. All patients with CMV reactivation received ganciclovir therapy until CMV titer became negative. Results: Day +30 total T cell recovery was significantly faster in MRD than CY-treated recipients (p=0.015) due principally to more robust CD8+ T cell recovery. CD4 T cell recovery remained below normal range in all groups through day +100. NK cells recovered to normal numbers at day +28 in all groups. Neither PTCy nor donor source significantly impacted the percentage of patients that recovered anti-CMV CD8+ T cells at each time interval (p = 0.8232). Excluding donors (D) and recipients (R) that were both negative, CMV/DEX+ T cells recovery was >7/mL in 4/5 MRD, 7/14 MUD, and 3/5 HAPLO by day +100. Among MRD recipients either D+ or R+ (n=5), 2 patients showed CMV reactivation within 40 days of transplant that was associated with <7 CMV/DEX+ T cells on day +30. Subsequent high (>90/mL) CMV/DEX T cell response in one patient shortened the duration of viremia to 10 days (vs. 16 days with poor responder) and 3 patients showed no CMV reactivation and a high CMV/DEX+ T cell response by day +60. For MUD CMV D+ and/or R+ recipients (n=14), 3 showed CMV reactivation within 50 days of transplant. All 3 patients had suboptimal CMV/DEX T cell response on day +30. Robust CMV/DEX+ T cell response on day +60 predicted shorter duration of viremia (20 days vs. average of 32 days). For HAPLO CMV D+ and/or R+ (n=5) recipients, 4 experienced CMV reactivation within 50 days of transplant. All patients had a <7 CMV/DEX+ T cells/mL +30. Robust CMV/DEX+ T cell response by day +60 was associated with shorter duration of viremia (range 7-21 days), while one patient with <7/mL CMV/DEX+ T cells had continued CMV viremia for 36 days. Conclusion: In this preliminary analysis, neither PTCy nor donor source significantly impacted the percentage of patients that recovered anti-CMV CD8+ T cells at each time interval. A weak CMV/DEX+ response (<7 cells/mL) on day +30 was consistent with increased risk of CMV reactivation (viremia) in all groups. A CMV/DEX+ T cell count ≥7 cells/mL was not immediately protective against CMV reactivation, but higher counts were associated with a shortened duration of viremia while on antiviral therapy. Conversely, subnormal counts were associated with a longer duration of viremia. This interim analysis suggests that CMV/DEX+ T cell enumeration is a useful biologic correlate for determining clinical response to antiviral therapy, and that donor-derived CMV specific T cell immunity is not further compromised with following PTCy in alternative donor HCT. Disclosures No relevant conflicts of interest to declare.

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