Expansion Of Effector Memory CD8 Research Articles

Abstract 5660: IGM-7354, an immunocytokine with IL-15 fused to an anti-PD-L1 IgM, induces NK and CD8+ T cell mediated cytotoxicity of PD-L1-positive tumor cells

Abstract Immunostimulatory cytokines are a promising immunotherapy for the treatment of advanced malignancies, but generally have been associated with severe toxicities when administered systemically. The recent development of antibody-cytokine fusion proteins, or immunocytokines, aims to localize cytokine activity to the tumor microenvironment and thus improve their therapeutic index. We have developed IGM-7354, a high affinity, high avidity anti-PD-L1 pentameric IgM antibody with an IL-15Rα chain and IL-15 fused to the joining (J) chain. The IGM-7354 immunocytokine was designed to deliver IL-15-mediated stimulation of NK and CD8+ T cells to PD-L1-expressing tumors and antigen-presenting cells, to enhance anti-tumor immune responses. The multivalent binding of IGM-7354 to PD-L1 provided a stronger binding avidity for human PD-L1 than the monovalent binding of IL-15 to IL-15Rb as confirmed in kinetic binding assays. In vitro IGM-7354 induced the proliferation of a cytotoxic T cell line responsive to IL-15 stimulation and enhanced the proliferation of NK and CD8+ T cells from healthy donor human PBMCs. In cytotoxicity assays with human PBMC and PD-L1+ cancer cell lines, IGM-7354 enhanced cancer cell killing through NK and CD8+ T cell expansion and cytotoxic activity, evidenced by Ki67 and Granzyme B upregulation in these cell populations. Next, in vivo pharmacodynamic studies were performed in two humanized mouse models: non-tumor-bearing BRGSF-HIS mice engrafted with human CD34+ cells, and PD-L1+ MDA-MB-231 tumor-bearing MHC-/- NSG mice engrafted with human PBMCs. In the BRGSF model, IGM-7354 increased NK cell activation and Granzyme B expression as well as NK and CD8+ T cell proliferation. In the tumor-bearing mouse model, IGM-7354 dose-dependently increased NK and CD8+ T cell proliferation in blood and infiltration of lymphocytes into the tumor. This pharmacodynamic activity correlated with IGM-7354 anti-tumor activity in the MDA-MB-231 model. Lastly, IGM-7354 increased the proliferation of NK and CD8+ T cells in cynomolgus monkeys and particularly induced the expansion of effector memory CD8+ T cells in the periphery. In summary, IGM-7354 induces NK and CD8+ T cell proliferation in both in vitro and in vivo preclinical models, resulting in the killing of PD-L1+ tumor cells. The strong avidity of IGM-7354 for PD-L1 may enhance IL-15 delivery to tumors and antigen-presenting cells and thus provide a more favorable safety profile. A Phase 1 clinical trial is planned. Citation Format: Thierry D. Giffon, Melanie Desbois, Poonam Yakkundi, Susan Calhoun, Keerthana Sekar, Carolyn Denson, Tasnim Kothambawala, Alexander Pearson, Sivani Pandey, Deepal Pandya, Rodnie Rosete, Daniel Machado, Pat Raichlen, Dean Ng, Abhinav R. Jain, Roel Funke, Eric Humke, Paul R. Hinton, Beatrice Wang, Bruce A. Keyt, Maya F. Kotturi, Angus M. Sinclair. IGM-7354, an immunocytokine with IL-15 fused to an anti-PD-L1 IgM, induces NK and CD8+ T cell mediated cytotoxicity of PD-L1-positive tumor cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5660.

Clonal expansion of resident memory T cells in peripheral blood of patients with non-small cell lung cancer during immune checkpoint inhibitor treatment

BackgroundImmune checkpoint inhibitors (ICIs) are an essential treatment for non-small cell lung cancer (NSCLC). Currently, the tumor-related intrinsic factors in response to ICIs have mostly been elucidated in tissue samples....

Late-onset enteric virus infection associated with hepatitis (EVAH) in transplanted SCID patients

Allogenic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) are potentially curative treatments for severe combined immunodeficiency (SCID). Late-onset posttreatment manifestations (such as persistent hepatitis) are not uncommon. We sought to characterize the prevalence and pathophysiology of persistent hepatitis in transplanted SCID patients (SCIDH+) and to evaluate risk factors and treatments. We used various techniques (including pathology assessments, metagenomics, single-cell transcriptomics, and cytometry by time of flight) to perform an in-depth study of different tissues from patients in the SCIDH+ group and corresponding asymptomatic similarly transplanted SCID patients without hepatitis (SCIDH-). Eleven patients developed persistent hepatitis (median of 6 years after HSCT or GT). This condition was associated with the chronic detection of enteric viruses (human Aichi virus, norovirus, and sapovirus) in liver and/or stools, which were not found in stools from the SCIDH- group (n= 12). Multiomics analysis identified an expansion of effector memory CD8+ Tcells with high type I and II interferon signatures. Hepatitis was associated with absence of myeloablation during conditioning, split chimerism, and defective B-cell function, representing 25% of the 44 patients with SCID having these characteristics. Partially myeloablative retransplantation or GT of patients with this condition (which we have named as "enteric virus infection associated with hepatitis") led to the reconstitution of T- and B-cell immunity and remission of hepatitis in 5 patients, concomitantly with viral clearance. Enteric virus infection associated with hepatitis is related to chronic enteric viral infection and immune dysregulation and is an important risk for transplanted SCID patients with defective B-cell function.

The Immune Landscape of Papillary Thyroid Cancer in the Context of Autoimmune Thyroiditis.

Simple SummaryThe association between papillary thyroid cancer and Hashimoto’s thyroiditis went through a long-standing human debate recently elucidated by the establishment of a novel mouse model. Papillary thyroid carcinoma is an excellent model for studying the tumor immune microenvironment because it is naturally accompanied by immune cells, making it a good candidate for the treatment with immune checkpoint inhibitors.Papillary thyroid cancer (PTC) often co-occurs with Hashimoto’s thyroiditis, an association that has long been reported in clinical studies, remaining controversial. Experimental evidence has recently shown that pre-existing thyroiditis has a beneficial effect on PTC growth and progression by a distinctive expansion of effector memory CD8 T cells. Although the link between inflammation and PTC might involve different components of the immune system, a deep characterization of them which includes T cells, B cells and tertiary lymphoid structures, Mye-loid cells, Neutrophils, NK cells and dendritic cells will be desirable. The present review article considers the role of the adaptive and innate immune response surrounding PTC in the context of Hashimoto’s thyroiditis. This review will focus on the current knowledge by in vivo and in vitro studies specifically performed on animals’ models; thyroid cancer cells and human samples including (i) the dual role of tumor-infiltrating lymphocytes; (ii) the emerging role of B cells and tertiary lymphoid structures; (iii) the role of myeloid cells, dendritic cells, and natural killer cells; (iv) the current knowledge of the molecular biomarkers implicated in the complex link between thyroiditis and PTC and the potential implication of cancer immunotherapy in PTC patients in the context of thyroiditis.

Abstract 3438: Enhanced NK and CD8+ T cell proliferation, tumor cytotoxicity and reversal of T cell exhaustion with IGM-7354, an anti-PD-L1 IgM antibody and IL-15 cytokine fusion

Abstract Anti-PD-1/PD-L1 therapies are efficacious in certain cancer indications, but often patients relapse following a primary response Therefore rational combinations are needed to enhance initial and durable responses of anti-PD-1/PD-L1 therapies. Immunostimulatory cytokine, IL-15 is an attractive combination partner to enhance anti-tumor NK and memory CD8+ T cell expansion and survival. We are developing IGM-7354, a high affinity, high avidity anti-PD-L1 pentameric IgM antibody with an IL-15Rα chain and IL-15 fused to the joining (J) chain, designed to deliver IL-15 to PD-L1 expressing tumors for enhancing anti-tumor immune responses. IGM-7354 was generated by grafting heavy chain variable regions of a high affinity humanized anti-PD-L1 IgG onto the IgM heavy chain framework, co-expressed with the light chain and the J chain which included a single IL-15Rα and IL-15 fusion. Binding ELISAs were performed using recombinant antigens. IGM-7354 bound human and cynomolgus monkey PD-L1 with similar affinities but did not bind to rat or mouse PD-L1. In addition, the IL-15 component of IGM-7354 bound to human and cynomolgus β chain of the trimeric IL-15 receptor with similar affinities, but with weaker binding affinity to rodent IL-15Rβ. Using in vitro assays with human and cynomolgus monkey PBMCs, IGM-7354 dose-dependently enhanced the proliferation of NK and CD8+ T cells. Furthermore, in an in vitro MLR setting, IGM-7354 was able to reverse T cell exhaustion beyond that of an IL-15/IL15Rα complex or anti-PD-L1 IgM or IgG alone, as demonstrated by an increase in activation and effector cytokine secretion. In vitro cytotoxicity and ADCC assays were performed with luciferase-tagged human cancer cell lines and PBMCs. IGM-7354 enhanced in vitro killing of PD-L1-expressing cancer cells by human PBMCs in monotherapy and in combination with other therapeutic agents. Efficacy and pharmacodynamic studies in an MDA-MB-231 xenograft mouse model showed dose-dependent increases in circulating NK and CD8+ T cells and tumor-infiltrating lymphocytes, which correlated with tumor regression. In cynomolgus monkeys, IGM-7354 markedly induced the proliferation of NK and CD8+ T cells in a dose-dependent manner with a preferential expansion of effector memory CD8+ T cells and γδ T cells in the periphery. IGM-7354 stimulates NK and CD8+ T cell expansion in vitro and in vivo plus induces tumor regressions in mouse tumor models in monotherapy or combination with various agents. This approach may enhance tumor localization of the immunostimulatory cytokine IL-15 through high affinity and high avidity binding to PD-L1 thereby improving anti-tumor responses and minimizing toxicity. Citation Format: Thierry Giffon, Melanie Desbois, Poonam Yakkundi, Keerthana Sekar, Marigold Manlusoc, Rodnie Rosete, Daniel Machado, Susan Calhoun, Tasnim Kothambawala, Dean Ng, Vu Tran, Avneesh Saini, Abhinav Jain, Beatrice Wang, Maya Kotturi, Bruce Keyt, Angus Sinclair. Enhanced NK and CD8+ T cell proliferation, tumor cytotoxicity and reversal of T cell exhaustion with IGM-7354, an anti-PD-L1 IgM antibody and IL-15 cytokine fusion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3438.

Pre-existing Thyroiditis Ameliorates Papillary Thyroid Cancer: Insights From a New Mouse Model.

Papillary thyroid cancer (PTC) often co-occurs with Hashimoto's thyroiditis, an association that has long been reported in clinical studies yet remains controversial. Some studies, in fact, have suggested a protective effect of thyroiditis while others have not. We generated a mouse model where PTC and thyroiditis develop in a predictable manner, combining the oncogenic drive of the BRAFv600E mutation (inducible by tamoxifen) to the thyroiditis susceptibility of the NOD.H2h4 strain (inducible by iodine). A total of 113 NOD.H2h4_TPO-CRE-ER_BRAFV600E mice (50 followed throughout lifetime and 63 sacrificed at 16 weeks post tamoxifen) were used to determine whether the PTC phenotype differs when thyroiditis precedes or coincides with the onset of PTC. Mice with pre-existing thyroiditis lived longer (median survival of 28.2 weeks post tamoxifen) than those with concomitant (25.6 weeks) or no (24.5 weeks) thyroiditis (P < 0.01 by Laplace regression). PTC developed less frequently (33%) in the pre-existing thyroiditis group than the concomitant (100%) or no (100%) thyroiditis groups (P < 0.001 by chi-squared) and showed less aggressive histopathological features. The intratumoral mononuclear cell infiltration was more prominent in mice with pre-existing thyroiditis (P = 0.002 vs the other groups) and sustained by a significant expansion of effector memory CD8 + T cells and CD19 + B cells. These findings shed light on the controversial PTC-thyroiditis association and emphasize the contribution of intratumoral T and B lymphocytes to the evolution of PTC.

Recombinant human IL-15 (rhIL-15) in combination with anti-PD-L1 (Avelumab) in SIV infected rhesus macaques leads to the expansion of a subset of CXCR3+PD1−/low CD8 T cells

Abstract The PD1/PD-L1 pathway contributes to the pathogenesis of HIV/SIV infection. Expression of PD1 by HIV/SIV-specific CD8 T cells can limit antiviral responses and expression of checkpoint receptors including PD1 by HIV infected cells can contribute to maintenance of viral reservoirs. In addition, reports have shown that IL-15 induces the expansion of effector memory CD8 T and NK cells. In this study, we hypothesized that expansion of memory CD8 T cells in the context of PD1/PD-L1 blockade may lead to enhanced anti-SIV responses. We design a study in which we evaluated the effect of rhIL-15 administered in cycles of ten days by continuous infusion in combination with weekly administration of anti-PD-L1 (Avelumab) over 24 weeks. After seven doses of anti-PD-L1 and completion of two cycles of rhIL15, cART therapy was interrupted and anti-PD-L1 administration continued to complete 24 weeks treatment. We found that administration of rhIL-15 in combination with anti-PD-L1 treatment was well tolerated. rhIL-15 infusions were associated with transient increases in proliferation of NK cells and effector memory CD8 T cells. rhIL-15/anti-PD-L1 treatment led to a sustained expression of CXCR3+ with low to undetectable expression of PD1on CD8 T cells, suggesting potential of increased tissue trafficking. Multidimensional single cell analysis showed that CXCR3+PD1−/low CD8 T cells secrete cytokine in response to viral antigens. Despite these clear biological effects, no impact was observed on rebound plasma viremia after cART discontinuation and during anti-PD-L1 administration. Futures studies should characterize the CXCR3+PD1−/low CD8 T cell subset expanded by this treatment to understand the potential impact of this subset in viral control.

Deep sequencing and flow cytometric characterization of expanded effector memory CD8+CD57+ T cells frequently reveals T-cell receptor Vβ oligoclonality and CDR3 homology in acquired aplastic anemia.

Oligoclonal expansion of CD8+ CD28− lymphocytes has been considered indirect evidence for a pathogenic immune response in acquired aplastic anemia. A subset of CD8+ CD28− cells with CD57 expression, termed effector memory cells, is expanded in several immune-mediated diseases and may have a role in immune surveillance. We hypothesized that effector memory CD8+CD28−CD57+ cells may drive aberrant oligoclonal expansion in aplastic anemia. We found CD8+CD57+ cells frequently expanded in the blood of aplastic anemia patients, with oligoclonal characteristics by flow cytometric Vβ usage analysis: skewing in 1–5 Vβ families and frequencies of immunodominant clones ranging from 1.98% to 66.5%. Oligoclonal characteristics were also observed in total CD8+ cells from aplastic anemia patients with CD8+CD57+ cell expansion by T-cell receptor deep sequencing, as well as the presence of 1–3 immunodominant clones. Oligoclonality was confirmed by T-cell receptor repertoire deep sequencing of enriched CD8+CD57+ cells, which also showed decreased diversity compared to total CD4+ and CD8+ cell pools. From analysis of complementarity-determining region 3 sequences in the CD8+ cell pool, a total of 29 sequences were shared between patients and controls, but these sequences were highly expressed in aplastic anemia subjects and also present in their immunodominant clones. In summary, expansion of effector memory CD8+ T cells is frequent in aplastic anemia and mirrors Vβ oligoclonal expansion. Flow cytometric Vβ usage analysis combined with deep sequencing technologies allows high resolution characterization of the T-cell receptor repertoire, and might represent a useful tool in the diagnosis and periodic evaluation of aplastic anemia patients. (Registered at clinicaltrials.gov identifiers: 00001620, 01623167, 00001397, 00071045, 00081523, 00961064)

Immune Protection by a Cytomegalovirus Vaccine Vector Expressing a Single Low-Avidity Epitope.

Experimental CMV-based vaccine vectors expressing a single MHC class I-restricted high-avidity epitope provided strong, T cell-dependent protection against viruses or tumors. In this study we tested the low-avidity epitope KCSRNRQYL, and show that a mouse CMV (MCMV) vector provides complete immune control of recombinant vaccinia virus expressing the same epitope if KCSRNRQYL is expressed within the immediate-early MCMV gene ie2 The same epitope expressed within the early M45 gene provided no protection, although MCMV vectors expressing the high-avidity epitope SSIEFARL induced protective immunity irrespective of gene expression context. Immune protection was matched by Ag-induced, long-term expansion of effector memory CD8 T cells, regardless of epitope avidity. We explained this pattern by observing regularities in Ag competition, where responses to high-avidity epitopes outcompeted weaker ones expressed later in the replicative cycle of the virus. Conversely, robust and early expression of a low-avidity epitope compensated its weak intrinsic antigenicity, resulting in strong and sustained immunity and immune protection.

Oligoclonal Expansion of Effector Memory CD8+CD57+ T Cells May Sustain Bone Marrow Destruction in Aplastic Anemia

The character of oligoclonal expansion of CD8+CD28- lymphocytes in aplastic anemia (AA), described by Risitano et al. (Blood, 2002 and Lancet, 2004), strongly suggests an antigen driving mechanism of T cell activation leading to destruction of hematopoietic stem and progenitor cells. In this study, we focused on a subset of CD8+CD28- T lymphocytes termed effector memory cells because of their high antigen-affinity and ability to be rapid activated after antigen stimulation. We investigated the frequency and oligoclonal expansion of effector CD28-CD57+ memory cells in CD4+ and CD8+ T subsets and the T cell receptor (TCR) Vβ repertoire by flow cytometry, and next-generation sequencing (NGS). Peripheral blood mononuclear cells from 20 AA patients and 14 healthy controls were evaluated for Vβ usage by flow cytometry. At the time of sampling, none of the patients had yet received immunosuppressive therapy. CD28+CD57- and CD28-CD57+ cells in CD4+ and CD8+ populations were assessed using the IOTest Beta Mark and a LSRII Fortessa cytometer for acquisition. The mean + 3SD of each Vβ group in controls was used as a cut-off to determine Vβ skewing in patients. When the frequencies of CD28+ and CD57+ cells in CD4+ and CD8+ subsets were compared, no differences were found between patients and controls (p=0.6125). Polyclonal expansion was described in CD8+CD28+, CD4+CD28+ and CD4+CD57+ T cells in 60%, 45% and 70% of patients, respectively. Using the mean of CD8+CD57+ cell frequency in controls as a cut-off, 12 of 20 patients displayed expansion of effector memory CD8+ cells and 11 of them (55% of all patients) showed expansion in 1 to 6 Vβ families with 1 to 4 immunodominant clones, while only 4 of 14 (29%) healthy controls displayed expansion of two Vβ families in expanded CD8+CD57+ cells without polyclonal expansion of CD8+CD28+ cells. In four cases (20% of all cases) of the remaining 8 patients whose cells did not display expanded CD8+CD57+ cells, there was expansion of 1 to 3 Vβ families with 1 dominant clone. These findings suggest activation of the immune response, polyclonal expansion of effector CD28+ compartments, and oligoclonal activation of effector memory CD8+ cells, regardless of frequency in peripheral blood. The frequency of CD8+CD57+ cells modestly correlated with the mean Vβ expansion in each patient (r2=0.5831, p<0.001). Also, we analyzed VDJ combinations and complementary region 3 (CDR3) sequences in CD4+ and CD8+ cells from 8 AA patients with CD8+CD57+ expansion in the ILLumina Hiseq 2000 sequencer. For the CD4+ compartment, patients were similar to healthy control CD4+ cells: frequencies of the most abundant clones less than 6%, CDR3 size profiles with Gaussian distribution and low degree of diversity (Simpson’s indexes range 0-1: 0 means infinite diversity, and 1 means no diversity). For CD8+ cells, 6 of 8 patients displayed a "skyscraper" Vβ/Jβ plot due to the presence of 1 to 3 dominant clones, with frequency greater than 10%, predominant classes in CDR3 size profile, and Simpson’s index similar to the CD8+CD57+ subset (p=0.1914). Analyzing CDR3 amino acid sequences for homology, we found that all the dominant sequences from patients were present at very low frequency in a healthy donor CD8+ cell pool (range, 0.12% - 53.6% vs 0.01% - 1.64%, p=0.0037), but no matches were described for the healthy CD8+CD57+ CDR3 repertoire. Only three CDR3 sequences were shared between patients. One of these CDR3 sequences (CSARDPPVSGTRGTDTQYF) was present in all patients and controls at very low frequency (mean expression, 5.01%), and it was the dominant clone in one patient, carried by TRBV20-1/TRBJ2-3 rearrangement at a frequency of 53.6%. Shared sequences were not found in reported viral TCR repertoires, nor in T cells recognizing peptide of myelin basic protein in multiple sclerosis, or synovial T cells from rheumatoid arthritis patients, nor matches were identified in T-large granular lymphocyte leukemia, AA, cancer or melanoma-derived TCR repertoires. Our data support the hypothesis of autologous immune-mediated attack leading to bone marrow destruction, likely triggered by autoantigens. Our results highlight the role of effector memory CD8+CD57+ T cells in sustaining an aberrant immune response during active disease. CD8+CD57+ cell expansion mirrors Vβ oligoclonal expansion, and Vβ flow cytometry should be useful in diagnosis and periodic evaluation of AA patients. DisclosuresFernandez Ibanez:GSK/Novartis: Research Funding. Young:Novartis: Research Funding.

Short-Lived Effector CD8 T Cells Induced by Genetically Attenuated Malaria Parasite Vaccination Express CD11c

Vaccination with a single dose of genetically attenuated malaria parasites can induce sterile protection against sporozoite challenge in the rodent Plasmodium yoelii model. Protection is dependent on CD8(+) T cells, involves perforin and gamma interferon (IFN-γ), and is correlated with the expansion of effector memory CD8(+) T cells in the liver. Here, we have further characterized vaccine-induced changes in the CD8(+) T cell phenotype and demonstrated significant upregulation of CD11c on CD3(+) CD8b(+) T cells in the liver, spleen, and peripheral blood. CD11c(+) CD8(+) T cells are predominantly CD11a(hi) CD44(hi) CD62L(-), indicative of antigen-experienced effector cells. Following in vitro restimulation with malaria-infected hepatocytes, CD11c(+) CD8(+) T cells expressed inflammatory cytokines and cytotoxicity markers, including IFN-γ, tumor necrosis factor alpha (TNF-α), interleukin-2 (IL-2), perforin, and CD107a. CD11c(-) CD8(+) T cells, on the other hand, expressed negligible amounts of all inflammatory cytokines and cytotoxicity markers tested, indicating that CD11c marks multifunctional effector CD8(+) T cells. Coculture of CD11c(+), but not CD11c(-), CD8(+) T cells with sporozoite-infected primary hepatocytes significantly inhibited liver-stage parasite development. Tetramer staining for the immunodominant circumsporozoite protein (CSP)-specific CD8(+) T cell epitope demonstrated that approximately two-thirds of CSP-specific cells expressed CD11c at the peak of the CD11c(+) CD8(+) T cell response, but CD11c expression was lost as the CD8(+) T cells entered the memory phase. Further analyses showed that CD11c(+) CD8(+) T cells are primarily KLRG1(+) CD127(-) terminal effectors, whereas all KLRG1(-) CD127(+) memory precursor effector cells are CD11c(-) CD8(+) T cells. Together, these results suggest that CD11c marks a subset of highly inflammatory, short-lived, antigen-specific effector cells, which may play an important role in eliminating infected hepatocytes.

Rabbit antithymocyte globulin induces rapid expansion of effector memory CD8 T cells without accelerating acute graft versus host disease

Rabbit antithymocyte globulin (Thymoglobulin®) is commonly used as graft-versus-host disease (GvHD) prophylaxis. Since we found similar total CD8 T cell numbers in patients with and without Thymoglobulin® therapy within the first six months after allogeneic hematopoietic stem cell transplantation, we have analyzed the reconstitution of the CD8 T cell compartment in detail. After T cell-depletion, higher and more sustained proliferative capacity of memory CD8 T cells resulted in their rapid expansion, whereas the fraction of naive CD8 T cells decreased. Importantly, this shift towards effector memory CD8 T cells did not accelerate the incidence of GvHD.

Transient and persistent effects of IL-15 on lymphocyte homeostasis in nonhuman primates

AbstractInterleukin-15 (IL-15) is a cytokine with potential therapeutic application in individuals with cancer or immunodeficiency to promote natural killer (NK)– and T-cell activation and proliferation or in vaccination protocols to generate long-lived memory T cells. Here we report that 10-50 µg/kg IL-15 administered intravenously daily for 12 days to rhesus macaques has both short- and long-lasting effects on T-cell homeostasis. Peripheral blood lymphopenia preceded a dramatic expansion of NK cells and memory CD8 T cells in the circulation, particularly a 4-fold expansion of central memory CD8 T cells and a 6-fold expansion of effector memory CD8 T cells. This expansion is a consequence of their activation in multiple tissues. A concomitant inverted CD4/CD8 T-cell ratio was observed throughout the body at day 13, a result of preferential CD8 expansion. Expanded T- and NK-cell populations declined in the blood soon after IL-15 was stopped, suggesting migration to extralymphoid sites. By day 48, homeostasis appears restored throughout the body, with the exception of the maintenance of an inverted CD4/CD8 ratio in lymph nodes. Thus, IL-15 generates a dramatic expansion of short-lived memory CD8 T cells and NK cells in immunocompetent macaques and has long-term effects on the balance of CD4+ and CD8+ T cells.

Interleukin-15 Increases Effector Memory CD8+T Cells and NK Cells in Simian Immunodeficiency Virus-Infected Macaques

Interleukin-15 (IL-15) in vitro treatment of peripheral blood mononuclear cells (PBMC) from human immunodeficiency virus (HIV)-infected individuals specifically enhances the function and survival of HIV-specific CD8+ T cells, while in vivo IL-15 treatment of mice preferentially expands memory CD8+ T cells. In this study, we investigated the in vivo effect of IL-15 treatment in 9 SIVmac251-infected cynomolgus macaques (low dose of IL-15, 10 microg/kg of body weight, n = 3; high dose of IL-15, 100 microg/kg, n = 3; control [saline], n = 3; dose administered twice weekly for 4 weeks). IL-15 treatment induced a nearly threefold increase in peripheral blood CD8+CD3- NK cells. Furthermore, CD8+ T-cell numbers increased more than twofold, mainly due to an increase in the CD45RA-CD62L- and CD45RA+CD62L- effector memory CD8+ T cells. Expression of Ki-67 in the CD8+ T cells indicated expansion of CD8+ T cells and not redistribution. IL-15 did not affect CD4+ T-cell, B-cell, and CD14+ macrophage numbers. No statistically significant differences in changes from baseline in the viral load were observed when control-, low-dose-, and high-dose-treated animals were compared. No clinical adverse effects were observed in any of the animals studied. The selective expansion of effector memory CD8+ T cells and NK cells by IL-15 further supports IL-15's possible therapeutic use in viral infections such as HIV infection.