Allelic variants of full-length VAR2CSA, the placental malaria vaccine candidate, differ in antigenicity and receptor binding affinity

Plasmodium falciparum-infected erythrocytes (IE) sequester in the placenta via surface protein VAR2CSA, which binds chondroitin sulfate A (CSA) expressed on the syncytiotrophoblast surface, causing placental malaria (PM) and severe adverse outcomes in mothers and their offspring. VAR2CSA belongs to the PfEMP1 variant surface antigen family; PfEMP1 proteins mediate IE adhesion and facilitate parasite immunoevasion through antigenic variation. Here we produced deglycosylated (native-like) and glycosylated versions of seven recombinant full-length VAR2CSA ectodomains and compared them for antigenicity and adhesiveness. All VAR2CSA recombinants bound CSA with nanomolar affinity, and plasma from Malian pregnant women demonstrated antigen-specific reactivity that increased with gravidity and trimester. However, allelic and glycosylation variants differed in their affinity to CSA and their serum reactivities. Deglycosylated proteins (native-like) showed higher CSA affinity than glycosylated proteins for all variants except NF54. Further, the gravidity-related increase in serum VAR2CSA reactivity (correlates with acquisition of protective immunity) was absent with the deglycosylated form of atypical M200101 VAR2CSA with an extended C-terminal region. Our findings indicate significant inter-allelic differences in adhesion and seroreactivity that may contribute to the heterogeneity of clinical presentations, which could have implications for vaccine design.

Targeting PRAME with TCR-Mimic CAR T Cells in AML

Chimeric antigen receptor (CAR) Ts have been effective in pre-B ALL, but their efficacy in AML has yet to be established. A significant barrier to effective CAR T therapy for AML is the substantial overlap of cell surface antigens expressed on AML and normal hematopoietic cells. To overcome this barrier, we profiled the transcriptome of over 3000 AML cases in children and young adults and contrasted this to normal hematopoietic tissues in search for AML-restricted targets (high expression in AML, silence in normal hematopoiesis). This led to the discovery of over 200 AML-restricted genes. Of these, Preferentially Expressed Antigen in Melanoma (PRAME) is among one of the highest expressing AML-restricted genes (Figure 1A) and, given its previous track record as a target for a variety of cancers, we selected this target for further assessment and therapeutic development in AML. However, PRAME is intracellular and therefore is inaccessible for targeting with conventional CAR T. Recently, a novel approach to target intracellular antigens was developed using TCR mimic (mTCR) antibodies, which recognize peptide/human leukocyte antigen (HLA) complexes on the tumor cell surface in a similar mode of recognition as authentic T Cell Receptors (TCRs). The Pr20 antibody was developed to recognize the PRAME ALY peptide in the context of HLA-A*02. Utilizing this Pr20 antibody, we developed a mTCR CAR T targeting PRAME and evaluated its preclinical efficacy in AML. The VL and VH sequences from Pr20 were used to construct the single-chain fragment variable domain of the 41-BB/CD3ζ CAR vector. We evaluated PRAME mTCR CAR T cells against OCI-AML-2 and THP-1 AML cell lines (PRAME +/HLA-A*02 +), K562 CML cell line (PRAME +/HLA-A*02 -) and HEK293T (293T) (PRAME -/HLA-A*02 +). Using a PE-conjugated Pr20 antibody, we confirmed that OCI-AML2 and THP-1 express PRAME ALY: HLA-A*02 but not K562 and 293T by flow cytometry (Figure 1B). As further confirmation, AML blasts in primary patient samples also stained with the Pr20 antibody (Figure 1C). For in-vivo studies, leukemia-bearing mice were treated with unmodified T or PRAME mTCR CAR T cells at 5x10 6 cells (1:1 CD4:CD8) per mouse 1 week following leukemia injection. Leukemia burden was measured weekly by bioluminescence IVIS imaging. Cells were treated with 10ng/mL of IFN-γ prior to co-incubation with T cells for 16 hours. PRAME mTCR CAR T cells demonstrated potent cytolytic activity against OCI-AML2 and THP1 but not against K562 or 293T cells, following co-incubation with target cells for 24 hours (Figure 1D). Consistent with potent, target-specific reactivity against PRAME ALY: HLA-A*02 positive cells, increased levels of IFN-γ, IL-2 and TNF-α were detected in cocultures of CAR T cells with OCI-AML2 and THP1 but not with K562 and 293T cells (Figure 1D). The cytolytic activity of PRAME mTCR CAR T cells extended to primary AML specimens expressing the PRAME ALY: HLA-A*02 antigen (data not shown). In-vivo efficacy of PRAME mTCR CAR T was demonstrated in OCI-AML2 and THP-1 CDX models (Figure 1E). Treatment with CAR T cells induced leukemia clearance and significantly reduced leukemia burden in OCI-AML2 and THP-1 xenograft mice, respectively, while treatment with unmodified T cells exhibited leukemia progression (Figure 1E). The anti-leukemia activity of CAR T cells resulted in enhanced survival in OCI-AML2 (p=0.0035) and THP-1 (p=0.0047) xenografts (Figure 1F). The in-vivo activity of PRAME mTCR CAR T cells was target specific, as treatment with CAR T cells did not affect leukemia burden and survival in K562 xenograft mice (Figure 1F). Given that IFN-γ promotes PRAME presentation, we investigated whether treatment of IFN-γ would enhance cytolytic activity of PRAME mTCR CAR T cells. OCI-AML2 and THP-1 cells pretreated with IFN-γ were more sensitive to cytolysis compared to untreated controls (Figure 1G). In this study, we demonstrate the therapeutic potential of targeting PRAME with mTCR CAR T cells in AML. We show potent, target-specific reactivity of PRAME mTCR CAR T cells against PRAME ALY: HLA-A*02 positive AML cells, both in-vitro and in-vivo. We further demonstrate that the activity of PRAME mTCR CAR T cells can be enhanced with IFN-γ treatment, providing a useful strategy to increase efficacy. Thus, the results presented provide a novel approach to target PRAME with CAR T cells and compelling data to evaluate PRAME mTCR CAR T cells in AML clinical trials. Figure 1 Figure 1. Disclosures Pardo: Hematologics, Inc.: Current Employment. Hylkema: Quest Diagnostics Inc: Current equity holder in publicly-traded company; Moderna: Current equity holder in publicly-traded company. Scheinberg: Eureka Therapeutics: Current equity holder in publicly-traded company.

179 CD8+CD69+ Expanded Tumor Infiltrating Lymphocytes from Soft Tissue Sarcoma Have Increased Tumor-Specific Functional Capacity

BackgroundAdoptive cell therapy (ACT) utilizing tumor infiltrating lymphocytes (TIL) has demonstrated durable responses in patients with metastatic melanoma and offers potential for other solid tumors. Preclinical experience with expanded TIL from soft tissue sarcoma (STS) demonstrates less frequent tumor-specific reactivity compared to melanoma samples, limiting the potential for efficacy.1 We hypothesized that CD69+ TIL have increased tumor-specific reactivity, which can be manipulated in culture, thereby offering an opportunity to enhance the antitumor effect of this cellular immunotherapy product.MethodsPatients were enrolled on an IRB-approved protocol and TIL were expanded from fresh surgical specimens. After enzymatic digestion, tumor single cell suspensions were cultured in media containing 10% human serum and IL-2 (6000IU/mL). Expanded TIL were then enriched for CD8+ using magnetic bead isolation and CD69+ by flow cytometry cell sorting (FACS). After co-culture with autologous tumor digest, functional capacity was compared between bulk TIL and enriched TIL by evaluation of IFN-gamma (IFNg) and Granzyme B (GzB) secretion. Capacity for direct tumor cytotoxicity was assessed by Cr51 assay after co-culture of autologous immortalized cell lines with expanded TIL subpopulations after enrichment.ResultsFollowing co-culture with autologous tumor digest, CD69+ TIL demonstrated increased IFNg secretion compared to CD69- TIL in 6 samples (1.4–4.2x, p<0.05). CD8+ enriched TIL (75% compared to bulk) had higher relative IFNg secretion in both CD69+ and CD69- subsets (4.2 and 5.8x, respectively, p<0.001). Maximal IFNg secretion was seen from TIL that were both CD69+ sorted and CD8+ enriched, demonstrating an synergistic effect (16.3x vs Bulk CD69-, 4.2x vs Bulk CD69+, 2.8x vs CD8 enriched CD69- ; p<0.001). Functional capacity was also assessed by GzB secretion with similar results. CD69+ TIL had increased relative secretion (1.8–2.2x) compared to CD69- TIL (p< 0.01). CD8+ enriched TIL had increased relative GzB secretion in both CD69- and CD69+ sorted fractions (1.4x, 1.2x, respectively, p<.05). CD69+ sorted and CD8+ enriched TIL demonstrated an additive effect (2.6x vs Bulk CD69-, p<0.01; 1.2x vs Bulk CD69+, p<0.05; 1.8x vs CD8 enriched CD69-, p<0.01). CD8+ enriched CD69+ sorted TIL had greater relative cytotoxicity (3x, p<0.05) at 40:1 E:T ratio against autologous tumor cell lines compared to bulk expanded TIL (figure 1).Abstract 179 Figure 1Functional capacity of CD69+ TIL is demonstrated by increased secretion of GzB (A) and IFNg (B) after co-culture with autologous tumor digest. CD69+ TIL have greater cytotoxicity against autologous immortalized cell lines compared to bulk TIL at 40:1 E:T ratio (C).ConclusionsTIL expanded from STS demonstrate greater tumor-specific functional capacity and cytotoxicity after CD8 enrichment and CD69+ FACS compared to bulk expanded TIL. These data validate the strategy to enhance CD8+CD69+ TIL during culture to yield a more efficacious cellular immunotherapy product.AcknowledgementsThis work was funded by NIH K08CA252642Trial Registration n/aReference1. Mullinax JE, Hall M, Beatty M, Weber AM, Sannasardo Z, Svrdlin T, Hensel J, Bui M, Richards A, Gonzalez RJ, Cox CA, Kelley L, Mulé JJ, Sarnaik AA, Pilon-Thomas S. Expanded Tumor-infiltrating Lymphocytes From Soft Tissue Sarcoma Have Tumor-specific Function. J Immunother 2021 Feb-Mar 01;44(2):63–70.Ethics ApprovalAbstract cites IRB-approved protocol in methods section.Consent n/a

178 Expansion of Tumor-Infiltrating Lymphocytes and Marrow-Infiltrating Lymphocytes from Pediatric Malignant Solid Tumors

BackgroundHigh-risk non-CNS pediatric malignant solid tumors (pMST) have unsatisfactory outcomes, and novel therapies are warranted. Adoptive cellular therapy (ACT) using tumor-infiltrating lymphocytes (TIL) has produced durable responses in melanoma, and improvements in TIL expansion have made ACT-TIL feasible for other solid tumors.1–3 Preclinical mouse models suggest that T-cells from bone marrow (marrow-infiltrating lymphocytes, MIL) have antitumor reactivity offering another source for ACT.4 5 To demonstrate feasibility of ACT in pMST we hypothesized that TIL/MIL can be expanded from these patients.MethodsPatients ≤21 years old undergoing standard-of-care pMST resection were enrolled on an IRB approved protocol. Fresh tumor (≥1 cm3) was collected and bone marrow (10 mL) was obtained when accessible from standard of care procedures. TIL/MIL were cultured in media containing IL-2 (6000 IU/mL). TIL were expanded from tumor fragment cultures (TFC, >1 mm3) or tumor digest. Select TIL samples were further expanded using a rapid expansion protocol (REP). Phenotype of expanded TIL (CD3, CD4, CD8 and CD56) was evaluated using flow cytometry. IFN- γ secretion, measured by ELISA assay, measured tumor-specific reactivity after co-culture with autologous tumor and TIL.ResultsTwenty samples were obtained between March 2019-May 2021. Two samples were ineligible (final pathology not pMST), leaving 18 samples for analysis. Five marrow samples were collected. TIL were expanded from 14/18 samples (78%) through TFC with median 5.17 x 10^6 cells (range 1.86 x 10^6–3.21 x 10^8). Average phenotype (%) of TFC-TIL were CD3 (63.17), CD4 (21.46), CD8 (46.19) and CD56 (32.68). 9/10 (90%) of samples successfully underwent REP with median 9.35 x 10^7 cells(range 2.49 x 10^7–5.86 x 10^8) final viable TIL and average fold-change 718.6 (median 458.6). Average phenotype (%) of post-REP TIL were CD3 (96.04), CD4 (75.04), CD8 (19.17) and CD56 (0.43). TIL were expanded from TFC of therapy-naïve (8/10, 80%) and pretreated (chemotherapy and checkpoint immunotherapy) samples (5/8, 63%). Seven samples had sufficient tissue to test tumor-specific reactivity; all were non-reactive. MIL pre-REP was expanded from four samples with median 9.55 x 10^6 cells (range 8.00 x 10^5–1.00 x 10^7). Average phenotype of expanded MIL (%) were CD3 (45.17), CD4 (24.46), CD8 (36.15) and CD56 (28.21) (table 1).Results of TIL and MIL expansion from 18 pMST samples. Abbreviations: Dx: diagnosis, pre-REP: pre-rapid expansion protocol, post-REP: post-rapid expansion protocol, PBMC: peripheral blood mononuclear cells, GNB: ganglioneuroblastoma, WT: Wilms tumor, OS: osteosarcoma, NB: neuroblastoma, IMT: inflammatory myofibroblastic tumor; ASPS: alveolar soft part sarcoma, SS: synovial sarcoma, ERMS: embryonal rhabdomyosarcoma, N: no systemic therapy, C: chemotherapy, I: immunotherapy, DNG: did not grow, N/A: not applicable, NR: non-reactiveAbstract 178 Table 1Expansion of TIL from pMSTConclusionsThis study demonstrates feasibility of pMST TIL expansion ex vivo. Due to tissue volume constraints inherent in pMST sampling, anti-tumor reactivity testing was not feasible for most patients. Determining optimal strategy for TIL-ACT in pMST will require further investigation regarding techniques for expanding tumor-specific TIL.AcknowledgementsThe authors would like to thank Swim Across America (www.swimacrossamerica.org) and the Ocala Royal Dames (www.ocalaroyaldames.org) for their generous support of this work.ReferencesRosenberg SA, Restifo NP. Adoptive cell transfer as personalized immunotherapy for human cancer. Science 2015;348(6230):62–68.Hall M, Mullinax JE, Royster E, et al. Expansion and characterization of tumor-infiltrating lymphocytes from human sarcoma. Journal of Immunotherapy of Cancer 2015;3(Suppl. 2):19.Mullinax JE, Hall M, Beatty M, et al. Expanded tumor-infiltrating lymphocytes from soft tissue sarcoma have tumor-specific function. J Immunother 2021;44(2):63–70.Feuerer M, Beckhove P, Bai L, et al. Therapy of human tumors in NOD/SCID mice with patient-derived reactivated memory T cells from bone marrow. Nat Med 2001;7(4):452–458.Feuerer M, Rocha M, Bai L, et al. Enrichment of memory T cells and other profound immunological changes in the bone marrow from untreated breast cancer patients. Int J Cancer 2001;92(1):96–105.Ethics ApprovalThis study was approved by the Johns Hopkins All Children’s Hospital IRB (#IRB00193453). Consent was obtained from the patient or parent, as appropriate for age, prior to participating in this study.

Anti-Carbamylated Fibrinogen Antibodies Might Be Associated With a Specific Rheumatoid Phenotype and Include a Subset Recognizing In Vivo Epitopes of Its γ Chain One of Which Is Not Cross Reactive With Anti-Citrullinated Protein Antibodies

To identify the targets recognized by anti-carbamylated protein antibodies (anti-CarP) in patients with early Rheumatoid Arthritis (RA), to study the cross-reactivity between anti-CarP and anti-citrullinated protein antibodies (ACPA) and to evaluate their prognostic value. 331 patients (184 RA and 147 other rheumatisms) from the Very Early Arthritis (VErA) French cohort were analyzed. We performed mass spectrometry analysis of RA sera displaying anti-CarP activity and epitope mapping of the carbamylated fibrinogen γ chain to identify immunodominant peptides. The specificity of these targets was studied using competition assays with the major antigens recognized by ACPA. The prognostic value of anti-carbamylated fibrinogen IgG antibodies (ACa-Fib IgG) was compared to that of anti-cyclic citrullinated peptide antibodies (anti-CCP) and anti-CarP using an in-house ELISA. Besides the α chain, the γ chain of fibrinogen, particularly one immunodominant epitope that has a specific reactivity, was identified as a circulating carbamylated target in sera. The prevalence of ACa-Fib was 37% at baseline and 10.9% for anti-CCP-negative RA. In anti-CCP-negative patients, ACa-Fib positivity was associated with a more inflammatory and erosive disease at baseline but not with rapid radiological progression, which remains strongly related to anti-CCP antibodies. Fibrinogen seems to be one of the antigens recognized in vivo by the anti-CarP response, particularly 2 epitopes of the γ chain, one of which is not cross reactive with ACPA. This specificity might be associated with a distinct clinical phenotype since ACa-Fib IgG were shown to be linked to systemic inflammation in very early RA but not to rapid radiological progression.

Anticancer Targets and Signaling Pathways Activated by Britannin and Related Pseudoguaianolide Sesquiterpene Lactones

Sesquiterpene lactones (SLs) are abundant in plants and display a large spectrum of bioactivities. The compound britannin (BRT), found in different Inula species, is a pseudoguaianolide-type SL equipped with a typical and highly reactive α-methylene-γ-lactone moiety. The bioproperties of BRT and related pseudoguaianolide SLs, including helenalin, gaillardin, bigelovin and others, have been reviewed. Marked anticancer activities of BRT have been evidenced in vitro and in vivo with different tumor models. Three main mechanisms are implicated: (i) interference with the NFκB/ROS pathway, a mechanism common to many other SL monomers and dimers; (ii) blockade of the Keap1-Nrf2 pathway, with a covalent binding to a cysteine residue of Keap1 via the reactive α-methylene unit of BRT; (iii) a modulation of the c-Myc/HIF-1α signaling axis leading to a downregulation of the PD-1/PD-L1 immune checkpoint and activation of cytotoxic T lymphocytes. The non-specific reactivity of the α-methylene-γ-lactone moiety with the sulfhydryl groups of proteins is discussed. Options to reduce or abolish this reactivity have been proposed. Emphasis is placed on the capacity of BRT to modulate the tumor microenvironment and the immune-modulatory action of the natural product. The present review recapitulates the anticancer effects of BRT, some central concerns with SLs and discusses the implication of the PD1/PD-L1 checkpoint in its antitumor action.

Serologic response to Borrelia antigens varies with clinical phenotype in children and young adults with Lyme disease

Lyme disease is commonly diagnosed by serologic response to Borrelia burgdorferi and related species, but the relationship between serologic targets and clinical features is unknown. We developed a multi-antigen Luminex-based panel and evaluated IgG responses in 527 children 1 to 21 years of age assessed for Lyme disease across 4 Pedi Lyme Net emergency departments, including 127 Lyme cases defined by either an erythema migrans (EM) lesion or positive C6 enzyme immunoassay followed by immunoblot and 400 patients considered clinical mimics. Of 42 antigens tested, 26 elicited specific reactivity in Lyme patients, without marked age-dependent variation. Children with single EM lesions typically lacked Borrelia -specific IgG. By principal component analysis, children with early disseminated and late Lyme disease clustered separately from clinical mimics and also from each other. Neurological disease and arthritis exhibited distinct serologic responses, with OspC variants overrepresented in neurological disease and p100, BmpA, p58 and p45 overrepresented in arthritis. Machine learning identified a 3-antigen panel (VlsE_Bb, p41_Bb, OspC_Bafz) that distinguished Lyme disease from clinical mimics with a sensitivity of 86.6% (95% confidence interval [CI] 80.3-92.1) and a specificity of 95.5% (95% CI 93.4-97.4). Sensitivity was much lower in early Lyme disease (38.5%, 95% CI 15.4-69.2). Interestingly, 17 children classified as Lyme mimics had a positive 3-antigen panel, suggesting that more comprehensive serologic analysis could help refine Lyme diagnosis. In conclusion, multiplex antigen panels provide a novel approach to understanding the immune response in Lyme disease, potentially helping to facilitate accurate diagnosis and to understand differences between clinical stages.

Antibody Response to SARS-CoV-2 Membrane Protein in Patients of the Acute and Convalescent Phase of COVID-19

Understanding the course of the antibody response directed to individual epitopes of SARS-CoV-2 proteins is crucial for serological assays and establishment of vaccines. Twenty-one synthetic peptides were synthesized that have ten amino acids overlap and cover the complete membrane (M) protein. Plasma samples from 32 patients having acute disease and 30 patients from the convalescent phase were studied. Only peptide M01 (aa 1–20) and to a lesser extent peptide M21 (aa 201–222) showed specific reactivity as compared to historical control plasma samples. Peptide M01 was recognized by IgM- (71.9%) and IgG-specific antibodies (43.8%) during the acute phase as early as day 8 PIO. In a longitudinal analysis, a higher reactivity was observed for the IgM response directed to peptide M01 following day 20 PIO as compared to earlier time points of the acute phase. In the convalescent phase, antibody reactivity to the two M-specific peptides was significantly lower (&lt;30% seropositivity). A fusion protein encoding major parts of RBD also showed higher rates of recognition during acute (50.0%) and lower rates in the convalescent phase (23.3%). Taken together, our results suggest that during the acute phase of COVID-19 antibodies are raised to two linear epitopes of the SARS-CoV-2 M protein, located at the very N- and C-termini, showing almost similar levels of reactivity as immunodominant linear epitopes derived from the spike and nucleocapsid protein. Anti-M is also present in the convalescent phase of COVID-19 patients, however at lower levels, with the N-terminus of the M protein as a preferred target.

A single full-length VAR2CSA ectodomain variant purifies broadly neutralizing antibodies against placental malaria isolates

Placental malaria (PM) is a deadly syndrome most frequent and severe in first pregnancies. PM results from accumulation of Plasmodium falciparum (Pf)-infected erythrocytes (IE) that express the surface antigen VAR2CSA and bind to chondroitin sulfate A (CSA) in the placenta. Women become PM-resistant over successive pregnancies as they develop anti adhesion and anti-VAR2CSA antibodies, supporting VAR2CSA as the leading PM-vaccine candidate. However, the first VAR2CSA subunit vaccines failed to induce broadly neutralizing antibody and it is still unclear whether naturally acquired protective antibodies target variant or conserved epitopes. This is crucial to determine whether effective vaccines will require incorporation of many or only a single VAR2CSA allele. Here, IgG from multigravidae was sequentially purified on five full-length VAR2CSA ectodomain variants, thereby depleting IgG reactivity to each. The five VAR2CSA variants purified ~0.7% of total IgG and yielded both strain-transcending and strain-specific reactivity to VAR2CSA and IE-surface antigen. IgG purified on the first VAR2CSA antigen displayed broad cross-reactivity to both recombinant and native VAR2CSA variants, and inhibited binding of all isolates to CSA. IgG remaining after depletion on all variants showed significantly reduced binding-inhibition activity compared to initial total IgG. These findings demonstrate that a single VAR2CSA ectodomain variant displays neutralizing epitopes shared by multiple parasites, including maternal isolates, and suggest that a broadly effective PM-vaccine can be achieved with a limited number of VAR2CSA variants.