scholarly journals Intergraft Variability in Nonhematopoietic Immunoregulatory Cell Number and Expression of Immune Checkpoint Inhibitor Receptors and Ligands in Both Allo- and Autografts: Potential Target for Intervention

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3382-3382
Author(s):  
Qingdong Guan ◽  
Scott Gilpin ◽  
James Doerksen ◽  
Lauren Bath ◽  
Tracey Lam ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Cell Number ◽  
Cell Dose ◽  
Cd34 Cells ◽  
Ifn Γ

Abstract Intergraft variability in nonhematopoietic immunoregulatory cell number and expression of immune checkpoint inhibitor receptors and ligands in both allo- and autografts: potential target for intervention Qingdong Guan,1-3 Scott Gilpin,3 James Doerksen,3 Lauren Bath,3 Tracey Lam,3 Kristjan Paulson,4 Pascal Lambert,4 Yun Li,1,3 Donna A.Wall1-4 1, Department of Pediatrics and Child Health, 2, Immunology, University of Manitoba; 3, Manitoba Center for Advanced Cell and Tissue Therapy; 4, CancerCare Manitoba The number of CD34+ hematopoietic stem/progenitor cells (HSC) in HSC products is the main and often sole characterization of the graft used in HSCT. However CD34+ cells make up only 0.3-5% of the graft with the rest of the cells being lymphocytes and immature myeloid and granulocytic cells, including myeloid-derived suppressor cells (MDSC). We examined a cohort of HSC products collected from 2010-2014. Filgrastim and chemotherapy was used to mobilize 60 multiple myeloma and 34 lymphoma patients. Filgrastim-mobilized healthy donor products used in allografts (N=68) was a comparator. Aliquots stored in liquid nitrogen were analyzed for cell phenotype with a focus on immunoregulatory populations. We found CD33+CD15-CD14+HLA-DR-/low monocytic (M-MDSC) ranged from 0-59% in the infused graft. Similarly CD3+T lymphocyte ranged from 2-80% in the graft. There were 10-50 fold more M-MDSC than CD34+ cells with the infused M-MDSC cell dose ranging from 0-600×106/kg (Fig 1). Similarly CD3+T cell dose ranged from 4-670×106/kg (Fig1). M-MDSC were functional as they could suppress T cell proliferation and IFN-γ secretion, but promote regulatory T cell development in vitro. We examined receptor-ligand relations between M-MDSC and T cells and markers of T exhaustion. M-MDSC expressed variable PD-L1 (19.3±13.9% for MM, 10.4±4.4% for lymphoma and 7.0±4.8% for allografts), and CD86 (48.3±17.1% for MM, 59.9±15.4% for lymphoma and 57.8±17.0% for allografts), the ligands for PD-1 and CTLA-4, respectively. Blocking PD-L1-PD-1 signaling pathway using anti-PD-L1 or anti-PD1 partially reversed the suppressive functions of M-MDSC. Compared to allografts, CD4+T and CD8+T cells in the autografts showed poor proliferation, decreased the secretion of IFN-γ and/or granzyme B, and increased inhibitory receptors PD-1 and CTLA-4 on their surface - markers of T cell exhaustion. Levels of PD-L1 and CD86 on M-MDSC were correlated with expression of inhibitory receptors PD-1 and CTLA-4 on T cells, respectively. Taken together, our pilot data showed variable numbers of M-MDSC are infused with HSC grafts. These cells have strong immune regulatory function in vitro. T cells in autografts have high levels of T cell exhaustion markers and are less functional. It indicated immune function may be enhanced by interfering with PD1/PDL1 or CTLA-4. The numbers of M-MDSC and T cells are in the range of a cellular therapy product and may be targeted for enhance/inactivation pre- or peri-transplant immune function. Figure 1. The infusion cell dose of CD34+ stem cells, M-MDSC and CD3+T. Disclosures No relevant conflicts of interest to declare.

scholarly journals 805 Clonal, activated CD8+ T cells recognizing cardiac alpha-myosin drive immune checkpoint inhibitor associated myocarditis in mice

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A842-A842
Author(s):  
Margaret Axelrod ◽  
Wouter Meijers ◽  
Elie Tannous ◽  
Xiaopeng Sun ◽  
Juan Qin ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Single Cell ◽  
Cell Lines ◽  
Cd8 T Cells ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Animal Experiments ◽  
Eligibility Criteria

BackgroundNearly half of all U.S. oncology patients meet FDA eligibility criteria to receive treatment with an immune checkpoint inhibitor (ICI). With increasing use of ICIs, preventing, diagnosing and treating immune-related adverse events (irAEs) are urgent clinical challenges. Myocarditis is an uncommon irAE, affecting < 1% of ICI-treated patients, but is highly fatal, with a mortality rate of nearly 50%. Genetically altered Pdcd1-/-Ctla4± mice die prematurely and specifically due to myocarditis. This model recapitulates the clinical and pathological features of ICI-myocarditis, including abundant cardiac infiltrating CD8+ T cells. The potential autoantigen(s) involved in ICI-myocarditis are unknown for both human disease and our murine model.MethodsWe used Pdcd1-/-Ctla4± mice on the C57BL6 background as a model of ICI-myocarditis. Single cell RNA and T cell receptor (TCR) sequencing was performed on sorted CD45+ cardiac immune cells from four affected Pdcd1-/-Ctla4± mice compared to six healthy wild type mice. The most three clonal TCRs (TCR-A, B, C), derived from two independent Pdcd1-/-Ctla4± mice, were reconstructed using stiTChR and transduced into reporter T cell lines for antigen discovery. Alpha-myosin was selected as a candidate autoantigen due to lack of presentation in the thymus. Reporter TCR-A, B, and C cells were screened using a library of overlapping 20 amino acid peptides derived from alpha-myosin in co-culture with bone marrow derived dendritic cells.ResultsTreatment with anti-CD8, but not anti-CD4, depleting antibodies rescues survival of Pdcd1-/-Ctla4± mice. Furthermore, adoptive transfer of splenocytes from Pdcd1-/-Ctla4± mice with myocarditis to Rag1-/- recipient mice was sufficient to induce fatal myocarditis. Single cell RNA/TCR sequencing on the cardiac immune infiltrate of Pdcd1-/-Ctla4± mice identified highly activated, clonal CD8+ T cells as the dominant cell population. The TCR-A cell line, the most clonal TCR identified in single cell TCR sequencing, activates NFAT, NFkB, and AP-1 reporters in response to the alpha-myosin epitope VIQYFASI. The TCR-B and TCR-C cell lines activate their reporters in response to the alpha myosin peptide DALLVIQWNIRAFMGVKNWP, indicating that alpha-myosin is an autoantigen in this mouse model of ICI-myocarditis.ConclusionsClonal, activated CD8+ T cells are critical for the development of ICI-myocarditis. Alpha-myosin is an autoantigen recognized by the most clonal cardiac CD8+ T cells. Efforts are currently underway to determine whether human TCRs derived from ICI-myocarditis samples recognize similar antigens. These studies are the first to identify a candidate autoantigen in ICI-myocarditis and may yield new insights into irAE pathogenesis.Ethics ApprovalAll animal experiments were in accordance with the VUMC Institutional Animal Care and Use Committee (IACUC), protocol # M2000067

scholarly journals Green Tea Catechin Is an Alternative Immune Checkpoint Inhibitor that Inhibits PD-L1 Expression and Lung Tumor Growth

Molecules ◽  
2018 ◽  
Vol 23 (8) ◽  
pp. 2071 ◽  
Author(s):  
Anchalee Rawangkan ◽  
Pattama Wongsirisin ◽  
Kozue Namiki ◽  
Keisuke Iida ◽  
Yasuhito Kobayashi ◽  
...  
Keyword(s):  
T Cells ◽  
Mrna Expression ◽  
Green Tea ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitors ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Checkpoint Inhibitors ◽  
Green Tea Catechin ◽  
Ifn Γ

The anticancer activity of immune checkpoint inhibitors is attracting attention in various clinical sites. Since green tea catechin has cancer-preventive activity in humans, whether green tea catechin supports the role of immune checkpoint inhibitors was studied. We here report that (−)-epigallocatechin gallate (EGCG) inhibited programmed cell death ligand 1 (PD-L1) expression in non–small-cell lung cancer cells, induced by both interferon (IFN)-γ and epidermal growth factor (EGF). The mRNA and protein levels of IFN-γ–induced PD-L1 were reduced 40–80% after pretreatment with EGCG and green tea extract (GTE) in A549 cells, via inhibition of JAK2/STAT1 signaling. Similarly, EGF-induced PD-L1 expression was reduced about 37–50% in EGCG-pretreated Lu99 cells through inhibition of EGF receptor/Akt signaling. Furthermore, 0.3% GTE in drinking water reduced the average number of tumors per mouse from 4.1 ± 0.5 to 2.6 ± 0.4 and the percentage of PD-L1 positive cells from 9.6% to 2.9%, a decrease of 70%, in lung tumors of A/J mice given a single intraperitoneal injection of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In co-culture experiments using F10-OVA melanoma cells and tumor-specific CD3+ T cells, EGCG reduced PD-L1 mRNA expression about 30% in F10-OVA cells and restored interleukin-2 mRNA expression in tumor-specific CD3+ T cells. The results show that green tea catechin is an immune checkpoint inhibitor.

645 Preclinical development of a novel colon-targeted therapeutic for the treatment of immune checkpoint inhibitor (ICI)-colitis

2020 ◽  
Vol 8 (Suppl 3) ◽  
pp. A682-A682
Author(s):  
Nazli Dizman ◽  
Milton L Greenberg ◽  
Andrew C Newman ◽  
Jonathan Skupsky ◽  
JoAnn Hsu ◽  
...  
Keyword(s):  
T Cells ◽  
Side Effects ◽  
Systemic Inflammation ◽  
Adoptive Transfer ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Transfer Model ◽  
Next Generation

BackgroundImmune Checkpoint Inhibitor (ICI) therapies have significantly improved overall survival in numerous cancers, but colitis has emerged as the most frequent dose-limiting toxicity associated with these therapies. Patients experiencing colitis side effects have to discontinue their cancer therapy to treat the colitis, which repositions life-threatening cancer. An ideal therapeutic would offer a colon-restricted approach to treating colitis side effects, while allowing patients to stay on their ICI therapy, an approach unavailable with currently approved therapies.MethodsTo test this localized approach for the treatment of ICI-mediated colitis, we have developed a new chemical entity as a next-generation candidate therapeutic designed for oral administration. Permeability was tested in predictive epithelial monolayers and confirmed in rodent pharmacokinetic studies. We tested the drug in the preclinical adoptive transfer model for colitis. In this model, immunodeficient mice are hosts for adoptive transfer of naïve CD4+ T cells. In the absence of regulatory T cells, the transferred cells drive systemic inflammation and migrate to the colon, causing disease. Without treatment, these mice develop signs of colitis including weight loss, altered crypt architecture and infiltration of the lamina propria by week four. Furthermore, we developed a live biopsy culture system to test drug effects on ICI-colitis patient biopsies obtained via colonoscopy.ResultsIn-vitro studies demonstrate that the drug has minimal toxicity and that it potently suppresses T cell proliferation and cytokine secretion. Permeability studies show a limited ability to cross the colonic mucosa restricting anti-inflammatory effects to sites of ulceration and active colitis. When colitis mice were given drug by oral gavage after colitis had developed, treated mice showed a significant increase in weight over controls and improved histological scores. Importantly, markers of systemic inflammation remained unchained, and the cancer-killing ability of the primary ICI therapy was preserved. Results of the live biopsy culture studies will be presented.ConclusionsThese preliminary studies demonstrate that the candidate therapeutic has potential to become a novel next-generation oral therapy for ICI-colitis because it effectively limits leukocyte function in-vitro and in-vivo with minimal systemic absorption and minimal expected side effects. Given the favorable drug profile and the rapid growth of ICI therapies, our colon-restricted colitis therapeutic has the potential to improve outcomes in a large number of cancer patients. We anticipate commencing first-in-human studies in Q4 of 2021.AcknowledgementsNoneEthics ApprovalThe study was approved by City of Hope Cancer Center Institutional Review Board with the approval number of 19304.

scholarly journals Immune checkpoint inhibitor-associated celiac disease

2020 ◽  
Vol 8 (1) ◽  
pp. e000958 ◽  
Author(s):  
Yousef Badran ◽  
Angela Shih ◽  
Donna Leet ◽  
Meghan J Mooradian ◽  
Alexandra Coromilas ◽  
...  
Keyword(s):  
T Cells ◽  
Celiac Disease ◽  
T Cell ◽  
Lamina Propria ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Γδ T Cells ◽  
T Cell Subsets ◽  
Programmed Death

BackgroundRare cases of immune checkpoint inhibitor (ICI)-associated celiac disease (ICI-CeD) have been reported, suggesting that disruption of tolerance mechanisms by ICIs can unmask celiac disease (CeD). This study aims to characterize the clinicopathological and immunophenotypic features of ICI-CeD in comparison to ICI-associated duodenitis (ICI-Duo) and usual CeD.MethodsA medical and pathological records search between 2015 and 2019 identified eight cases of ICI-CeD, confirmed by tTG-IgA. Nine cases of ICI-Duo, 28 cases of moderate CeD, as well as 5 normal controls were used as comparison groups. Clinical information was collected from the electronic medical records. Immunohistochemistry for CD3, CD8, T-cell receptor gamma/delta (γδ), programmed death ligand 1 (PD-L1), and programmed death 1 (PD-1) were performed, with quantification of intraepithelial lymphocyte (IEL) subsets in three well-oriented villi. CD68, PD-L1, and PD-1 were assessed as a percentage of lamina propria surface area infiltrated by positive cells. Statistical significance was calculated by the Student’s t-test and Fisher’s exact test.ResultsThe eight patients with ICI-CeD (F:M=1:3) and nine patients with ICI-Duo (F:M=5:4) presented similarly with diarrhea (13/17) and abdominal pain (11/17) after a median of 1.6 months on ICI therapy. In patients with ICI-CeD, tTG-IgA ranged from 104 to >300 IU/mL. Histological findings in ICI-CeD and ICI-Duo were similar and included expansion of the lamina propria, active neutrophilic duodenitis, variably increased IELs, and villous blunting. Immunohistochemistry showed that the average number of IELs per 100 enterocytes is comparable between ICI-CeD and ICI-Duo, with increased CD3+ CD8+ T cells compared with normal duodenum but decreased γδ T cells compared with CeD. Average PD-L1 percentage was 9% in ICI-CeD and 18% in ICI-Duo, in comparison to <1% in CeD and normal duodenum; average PD-1 percentage was very low to absent in all cases (<3%). On follow-up, five patients with ICI-CeD improved on a gluten-free diet (GFD) as the sole therapeutic intervention (with down-trending tTG-IgA) while the other three required immunosuppression. All patients who developed ICI-Duo received immunosuppression with variable improvement in symptoms.ConclusionsICI-CeD resembles ICI-Duo clinically and histologically but shares the serological features and response to gluten withdrawal with classic CeD. Immunophenotyping of IELs in ICI-CeD and ICI-Duo also shows similar CD3, CD8, γδ T cell subsets, and PD-L1 populations, all of which differed quantitatively from usual CeD. We conclude that ICI-CeD is biologically similar to ICI-Duo and is likely a variant of ICI-Duo, but treatment strategies differ, with ICI-CeD often improving with GFD alone, whereas ICI-Duo requires systemic immunosuppression.

scholarly journals Tumor-Infiltrating PD-1hiCD8+-T-Cell Signature as an Effective Biomarker for Immune Checkpoint Inhibitor Therapy Response Across Multiple Cancers

2021 ◽  
Vol 11 ◽  
Author(s):  
Zhenyu Yang ◽  
Yulan Deng ◽  
Jiahan Cheng ◽  
Shiyou Wei ◽  
Hao Luo ◽  
...  
Keyword(s):  
Lung Cancer ◽  
T Cells ◽  
T Cell ◽  
Immune Cells ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Therapy Response ◽  
Rna Seq ◽  
Cancer Types

BackgroundStratification of patients who could benefit from immune checkpoint inhibitor (ICI) therapy is of much importance. PD-1hiCD8+ T cells represent a newly identified and effective biomarker for ICI therapy response biomarker in lung cancer. Accurately quantifying these T cells using commonly available RNA sequencing (RNA-seq) data may extend their applications to more cancer types.MethodWe built a transcriptome signature of PD-1hiCD8+ T cells from bulk RNA-seq and single-cell RNA-seq (scRNA-seq) data of tumor-infiltrating immune cells. The signature was validated by flow cytometry and in independent datasets. The clinical applications of the signature were explored in non-small-cell lung cancer, melanoma, gastric cancer, urothelial cancer, and a mouse model of breast cancer samples treated with ICI, and systematically evaluated across 21 cancer types in The Cancer Genome Atlas (TCGA). Its associations with other biomarkers were also determined.ResultsSignature scores could be used to identify the PD-1hiCD8+ T subset and were correlated with the fraction of PD-1hiCD8+ T cells in tumor tissue (Pearson correlation, R=0.76, p=0.0004). Furthermore, in the scRNA-seq dataset, we confirmed the capability of PD-1hiCD8+ T cells to secrete CXCL13, as well as their interactions with other immune cells. In 581 clinical samples and 204 mouse models treated with ICIs, high signature scores were associated with increased survival, and the signature achieved area under the receiver operating characteristic curve scores of 0.755 (ranging from 0.61 to 0.91) in predicting therapy response. In TCGA pan-cancer datasets, our signature scores were consistently correlated with therapy response (R=0.78, p&lt;0.0001) and partially explained the diverse response rates among different cancer types. Finally, our signature generally outperformed other mRNA-based predictors and showed improved predictive performance when used in combination with tumor mutational burden (TMB). The signature score is available in the R package “PD1highCD8Tscore” (https://github.com/Liulab/PD1highCD8Tscore).ConclusionThrough estimating the fraction of the PD-1hiCD8+ T cell, our signature could predict response to ICI therapy across multiple cancers and could serve as a complementary biomarker to TMB.

scholarly journals A human CD137×PD-L1 bispecific antibody promotes anti-tumor immunity via context-dependent T cell costimulation and checkpoint blockade

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Cecile Geuijen ◽  
Paul Tacken ◽  
Liang-Chuan Wang ◽  
Rinse Klooster ◽  
Pieter Fokko van Loo ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Bispecific Antibody ◽  
Checkpoint Inhibitor ◽  
Checkpoint Inhibitors ◽  
Clinical Activity ◽  
Functional Screening ◽  
Anti Tumor Activity

AbstractImmune checkpoint inhibitors demonstrate clinical activity in many tumor types, however, only a fraction of patients benefit. Combining CD137 agonists with these inhibitors increases anti-tumor activity preclinically, but attempts to translate these observations to the clinic have been hampered by systemic toxicity. Here we describe a human CD137xPD-L1 bispecific antibody, MCLA-145, identified through functional screening of agonist- and immune checkpoint inhibitor arm combinations. MCLA-145 potently activates T cells at sub-nanomolar concentrations, even under suppressive conditions, and enhances T cell priming, differentiation and memory recall responses. In vivo, MCLA-145 anti-tumor activity is superior to immune checkpoint inhibitor comparators and linked to recruitment and intra-tumor expansion of CD8 + T cells. No graft-versus-host-disease is observed in contrast to other antibodies inhibiting the PD-1 and PD-L1 pathway. Non-human primates treated with 100 mg/kg/week of MCLA-145 show no adverse effects. The conditional activation of CD137 signaling by MCLA-145, triggered by neighboring cells expressing >5000 copies of PD-L1, may provide both safety and potency advantages.

scholarly journals Deep immune profiling reveals targetable mechanisms of immune evasion in immune checkpoint inhibitor-refractory glioblastoma

2021 ◽  
Vol 9 (6) ◽  
pp. e002181
Author(s):  
Erin F Simonds ◽  
Edbert D Lu ◽  
Oscar Badillo ◽  
Shokoufeh Karimi ◽  
Eric V Liu ◽  
...  
Keyword(s):  
T Cells ◽  
Tumor Cells ◽  
Immune Evasion ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Prolonged Survival ◽  
Tumor Associated Macrophages ◽  
The Brain ◽  
Immune Profiling

BackgroundGlioblastoma (GBM) is refractory to immune checkpoint inhibitor (ICI) therapy. We sought to determine to what extent this immune evasion is due to intrinsic properties of the tumor cells versus the specialized immune context of the brain, and if it can be reversed.MethodsWe used CyTOF mass cytometry to compare the tumor immune microenvironments (TIME) of human tumors that are generally ICI-refractory (GBM and sarcoma) or ICI-responsive (renal cell carcinoma), as well as mouse models of GBM that are ICI-responsive (GL261) or ICI-refractory (SB28). We further compared SB28 tumors grown intracerebrally versus subcutaneously to determine how tumor site affects TIME and responsiveness to dual CTLA-4/PD-1 blockade. Informed by these data, we explored rational immunotherapeutic combinations.ResultsICI-sensitivity in human and mouse tumors was associated with increased T cells and dendritic cells (DCs), and fewer myeloid cells, in particular PD-L1+ tumor-associated macrophages. The SB28 mouse model of GBM responded to ICI when grown subcutaneously but not intracerebrally, providing a system to explore mechanisms underlying ICI resistance in GBM. The response to ICI in the subcutaneous SB28 model required CD4 T cells and NK cells, but not CD8 T cells. Recombinant FLT3L expanded DCs, improved antigen-specific T cell priming, and prolonged survival of mice with intracerebral SB28 tumors, but at the cost of increased Tregs. Targeting PD-L1 also prolonged survival, especially when combined with stereotactic radiation.ConclusionsOur data suggest that a major obstacle for effective immunotherapy of GBM is poor antigen presentation in the brain, rather than intrinsic immunosuppressive properties of GBM tumor cells. Deep immune profiling identified DCs and PD-L1+ tumor-associated macrophages as promising targetable cell populations, which was confirmed using therapeutic interventions in vivo.

Abstract LB037:89ZED88082A PET imaging to visualize CD8+T cells in patients with cancer treated with immune checkpoint inhibitor

2021 ◽  
Author(s):  
Laura Kist de Ruijter ◽  
Pim P. van de Donk ◽  
Jahlisa S. Hooiveld-Noeken ◽  
Danique Giesen ◽  
Alexander Ungewickell ◽  
...  
Keyword(s):  
T Cells ◽  
Cd8 T Cells ◽  
Pet Imaging ◽  
Immune Checkpoint ◽  
Immune Checkpoint Inhibitor ◽  
Checkpoint Inhibitor ◽  
Patients With Cancer

scholarly journals Gamma Interferon Production, but Not Perforin-Mediated Cytolytic Activity, of T Cells Is Required for Prevention of Toxoplasmic Encephalitis in BALB/c Mice Genetically Resistant to the Disease

2004 ◽  
Vol 72 (8) ◽  
pp. 4432-4438 ◽  
Author(s):  
Xisheng Wang ◽  
Hoil Kang ◽  
Takane Kikuchi ◽  
Yasuhiro Suzuki
Keyword(s):  
T Cells ◽  
T Cell ◽  
Nude Mice ◽  
Genetic Resistance ◽  
Cytolytic Activity ◽  
Gamma Interferon ◽  
Toxoplasmic Encephalitis ◽  
Wild Type ◽  
Ifn Γ

ABSTRACT We previously showed the requirement of both T cells and gamma interferon (IFN-γ)-producing non-T cells for the genetic resistance of BALB/c mice to the development of toxoplasmic encephalitis (TE). In order to define the role of IFN-γ production and the perforin-mediated cytotoxicity of T cells in this resistance, we obtained immune T cells from spleens of infected IFN-γ knockout (IFN-γ−/−), perforin knockout (PO), and wild-type BALB/c mice and transferred them into infected and sulfadiazine-treated athymic nude mice, which lack T cells but have IFN-γ-producing non-T cells. Control nude mice that had not received any T cells developed severe TE and died after discontinuation of sulfadiazine treatment due to the reactivation of infection. Animals that had received immune T cells from either wild-type or PO mice did not develop TE and survived. In contrast, nude mice that had received immune T cells from IFN-γ−/− mice developed severe TE and died as early as control nude mice. T cells obtained from the spleens of animals that had received either PO or wild-type T cells produced large amounts of IFN-γ after stimulation with Toxoplasma gondii antigens in vitro. In addition, the amounts of IFN-γ mRNA expressed in the brains of PO T-cell recipients did not differ from those in wild-type T-cell recipients. Furthermore, PO mice did not develop TE after infection, and their IFN-γ production was equivalent to or higher than that of wild-type animals. These results indicate that IFN-γ production, but not perforin-mediated cytotoxic activity, by T cells is required for the prevention of TE in genetically resistant BALB/c mice.

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