Abstract LB-070: Immune monitoring of PNK-007, an allogeneic, off the shelf NK cell in a Phase I study of acute myeloid leukemia

Celularity has developed a GMP platform for generating Placenta-derived intermediate Natural Killer cells (PNK-007): an allogeneic cytotoxic NK cell product culture-expanded and differentiated from placental CD34+ progenitor cells. In a 10 patient relapsed/refractory AML phase I study, PNK-007 infusion was evaluated following Cyclophosphamide-Fludarabine (Cy-Flu) conditioning treatment. Patients received a single PNK-007 infusion of 1 million (M) cells/kg, 3M cells/kg, or 10M cells/kg followed by rhIL-2 administered subcutaneously at 6M units every other day for up to 6 doses to facilitate PNK-007 persistence and expansion. Here, we report PNK-007 cell persistence, AML monitoring, and broader immune profiling from Phase I translational studies.

PNK-007 persistence in the blood was observed between 7 and 28 days post infusion in patients dosed ≥ 3M cells/kg. Functional analysis of PNK-007 isolated from the blood of one patient indicated post-infusion NK cell effector activity. This included sustained expression of NKp30, NKp46, and DNAM-1 NK cell activating receptors. CD94, CD11a, and CD16 expression were increased relative to the pre-infusion cell product. CD57 and KIRs were absent at infusion, but were found on a subset of PNK-007 post-infusion indicating further NK maturation in vivo. Negligible expression of immunoinhibitory checkpoint receptors was observed on PNK-007 14 days post-infusion including PD-1, TIM3, and LAG3. Post-infusion PNK-007 cells stained positive for granzyme B, perforin, and secreted IFNγ, but not TNFα in response to acute activation.

In the month following Cy-Flu conditioning, we observed limited reconstitution of myeloid and lymphoid cells, consistent with other reports investigating this patient population. T cells at day 7 were 35-65% CD4+Foxp3+ and sustained T cell expansion in two patients beyond day 14 was associated with elevated PD-1 expression. Patients were B and NK cell deficient and showed negligible monocyte reconstitution alongside neutropenia. Elevated monocyte and neutrophil counts in two patients occurred in the context of significantly increased AML burden in the blood. In those patients, between 25-50% of monocytes did not express MHC-II consistent with myeloid-derived suppressor cells.

Our translational studies allow us to monitor PNK-007 cell persistence and maturation in addition to characterizing broader immune reconstitution from clinical samples. PNK-007 maturation data from this study are consistent with our preclinical models. We further show in this patient population that immune reconstitution appears compromised following Cy-Flu conditioning. Our data identify kinetics of PNK-007 persistence alongside hematopoietic recovery and AML disease.

Citation Format: William van der Touw, Lin Kang, Julie M. Curtsinger, Vanessa Voskinarian-Berse, Bhavani Stout, Mohamad Hussein, Sarah A. Cooley, Jeffrey S. Miller, Robert Hariri, Xiaokui Zhang. Immune monitoring of PNK-007, an allogeneic, off the shelf NK cell in a Phase I study of acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-070.

Bispecific ligand-directed toxin targeting CD22 and CD19 (DT2219) for refractory B-cell malignancies: Results of phase I-II trial

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Background: The novel bispecific toxin DT2219 consists of a fusion between the catalytic domain of diphtheria toxin (DT) and single-chain variable fragments (scFV) of antibodies targeting human CD19 and CD22. Methods: The primary objective of Phase I Dose was to determine DT2219 dose which is well tolerated on an 8 dose schedule (days 1, 3, 5, 8 and day 15, 17, 19 and 22). Phase II Extension aimed to establish a preliminary estimate of overall response at day 29 in patients stratified to Arm A (relapsed/refractory B-cell lymphoma) and Arm B (B-cell leukemia). Baseline serum level of neutralizing antibody (NA) against diphteria toxin below 50% was required for eligibility. Results: Eighteen patients (NHL n = 12; ALL n = 6) at median age 65 years (range 50-83 yrs) with relapse/refractory disease and confirmed expression of CD19 and/or CD22 were enrolled. Treatment was well tolerated at 60 mcg/kg x 8 doses and the most common adverse events included capillary leak sy, elevated AST/ALT, low albumin, weight gain and leukopenia. All were Gr 1-2 and resolved after 3-5 days allowing day 15 DT2219 administration. There were no neutropenic fever or immune mediated adverse events. Four patients experienced dose limiting toxicity at dose 80 μg/kg/day: Gr 4 capillary leak syndrome (n = 1), Gr 3 LFTs abnormalities (n = 2) and Gr 4 thrombocytopenia > 7 days duration (n = 1). Thirteen patients were evaluable for response and 3 experienced objective clinical benefit. One patient with primary refractory pre-B acute lymphoblastic leukemia achieved complete remission after 1st cycle. Two patients with transformed lymphoma demonstrated transient tumor shrinkage, however, DT2219 therapy was discontinued due to DLT and increased NA titer after 1st cycle (pre C1 28%, pre C2 108%). Correlative studies showed a low incidence of neutralizing antibody in NHL patients recently exposed to Rituximab. Conclusions: We have established the biologically active dose of DT2219 at 60 μg/kg/day ×8 doses. Further development of DT2219 includes combination with rituximab (to reduce NA formation) and synergistic combinations against B-cell malignancies. Clinical trial information: NCT02370160.

Haploidentical natural killer cells induce remissions in non-Hodgkin lymphoma patients with low levels of immune-suppressor cells

We report a novel phase 2 clinical trial in patients with poor prognosis refractory non-Hodgkin lymphoma (NHL) testing the efficacy of haploidentical donor natural killer (NK) cell therapy (NK dose 0.5-3.27 × 107 NK cells/kg) with rituximab and IL-2 (clinicaltrials.gov NCT01181258). Therapy was tolerated without graft-versus-host disease, cytokine release syndrome, or neurotoxicity. Of 14 evaluable patients, 4 had objective responses (29%; 95% CI 12-55%) at 2 months: 2 had complete response lasting 3 and 9 months. Circulating donor NK cells persisted for at least 7 days after infusion at the level 0.6-16 donor NK cells/µl or 0.35-90% of total CD56 cells. Responding patients had lower levels of circulating host-derived Tregs (17 ± 4 vs. 307 ± 152 cells/µL; p = 0.008) and myeloid-derived suppressor cells at baseline (6.6 ± 1.4% vs. 13.0 ± 2.7%; p = 0.06) than non-responding patients. Lower circulating Tregs correlated with low serum levels of IL-10 (R 2 = 0.64; p < 0.003; n = 11), suggestive of less immunosuppressive milieu. Low expression of PD-1 on recipient T cells before therapy was associated with response. Endogenous IL-15 levels were higher in responders than non-responding patients at the day of NK cell infusion (mean ± SEM: 30 ± 4; n = 4 vs. 19.0 ± 4.0 pg/ml; n = 8; p = 0.02) and correlated with day 14 NK cytotoxicity as measured by expression of CD107a (R 2 = 0.74; p = 0.0009; n = 12). In summary, our observations support development of donor NK cellular therapies for advanced NHL as a strategy to overcome chemoresistance. Therapeutic efficacy may be further improved through disruption of the immunosuppressive environment and infusion of exogenous IL-15.

Postthaw characterization of umbilical cord blood: markers of storage lesion

BACKGROUND

The continued growth in the uses of umbilical cord blood (UCB) will require the development of meaningful postthaw quality assays. This study examines both conventional and new measures for assessing UCB quality after long-term storage.

STUDY DESIGN AND METHODS

The first arm of the study involved thawing UCB in storage for short (approx. 1 year) and long periods of time (>11 years). Conventional postthaw measures (colony-forming units [CFU], total nucleated cell counts, CD34+45+) were quantified in addition to apoptosis. The second arm of the study involved taking units stored in liquid nitrogen and imposing a storage lesion by storing the units in -80°C for various periods of time. After storage lesion, the units were thawed and assessed.

RESULTS

In the first arm of the study, there was little difference in the postthaw measures between UCB stored for short and long periods of time. There was a slight increase in the percentage of CD34+45+ cells with time in storage and a reduction in the number of cells expressing apoptosis markers. When moved from liquid nitrogen to -80°C storage, the nucleated cell count varied little but there was a distinct decrease in frequency of CFUs and increase in percentage of cells expressing both early and late markers of apoptosis.

CONCLUSION

Nucleated cell counts do not reflect damage to hematopoietic progenitors during long-term storage. Expression of caspases and other markers of apoptosis provide an early biomarker of damage during storage, which is consistent with other measures such as CFU and percentage of CD34+45+ cells.

Abstract 4082: CD47 blockade to enhance adaptive anti-tumor immune responses

The success of immunotherapy has been hindered by the ability of tumors to evade or inhibit the host immune system. One strategy tumors use to achieve this is upregulation of CD47, a cell surface protein that delivers a “don't eat me” signal. CD47 binds to SIRP-alpha on the surface of macrophages and disables their phagocytic function. Previous data showed CD47 blockade enhanced phagocytosis of tumor cells in vitro and improved survival of mice transplanted with human tumors. However, CD47 blockade has yet to be examined in a fully syngeneic system where the potential for tumor phagocytosis by macrophages and/or dendritic cells to promote presentation of tumor antigens to T cells can be defined. It has been reported that CD47 blockade can hinder T cell activation; however, this also has not been examined in a syngeneic system. Our hypothesis was that inducing tumor cell phagocytosis by CD47 blockade would enhance T-cell-mediated anti-tumor responses. Our data show that CD47 was expressed on the EL4 thymoma and B16-F10 melanoma cell lines that are syngeneic to H-2b, as well as on their ovalbumin-expressing derivatives EG7 and B16-OVA. CD47 also was expressed on CD8+ T cells and was further upregulated upon stimulation, suggesting it might play a role in immune effector function. However, in our hands CD47 blockade using antibody MIAP-301 did not inhibit activation of CD8+ T cells in vitro, and in preliminary experiments, CD47 blockade appeared to enhance activation of antigen-specific CD8+ T cells in vivo. Ongoing work is evaluating the effects of CD47 blockade and phagocytosis on antigen presentation in vitro and the effects of CD47 blockade on the generation of tumor-specific CD4 and CD8 T cells in vivo. We also plan to confirm that T cells activated under conditions of CD47 blockade can recognize endogenous tumor antigens to which there may be self-tolerance.

Supported by an HHMI Medical Student Fellowship (to KA), by the GREYlong Foundation, and by grant P01 AI035296 (to MFM).

Citation Format: Katie L. Anderson, Daisuke Ito, Debra C. Lins, Julie M. Curtsinger, Matthew F. Mescher, Jaime F. Modiano. CD47 blockade to enhance adaptive anti-tumor immune responses. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4082. doi:10.1158/1538-7445.AM2014-4082

Randomized phase II study of IL-2 with or without an allogeneic large multivalent immunogen vaccine for the treatment of stage IV melanoma

OBJECTIVE

To evaluate the activity of interleukin-2 (IL-2) in combination with allogeneic large multivalent immunogen (LMI) vaccine, prepared by immobilizing SK23-CD80 melanoma cell line plasma membrane on 5-μm-diameter silica beads, in patients with melanoma.

METHODS

Twenty-one patients with metastatic melanoma were randomly assigned to an IL-2 alone control group or an IL-2 plus LMI vaccine treatment group. The primary objective was to evaluate the progression-free survival (PFS) of each group. Secondary clinical objectives included median overall survival (OS) and 1- and 2-year rates of OS.

RESULTS

Treatment was very well tolerated. Median PFS was no different between the treatment arm (2.20 mo) and control arm (1.95 mo). Median OS was also similar for the treatment arm (11.89 mo) and control arm (9.97 mo).

CONCLUSIONS

This study failed to demonstrate that allogeneic LMI vaccine and low-dose IL-2 improved survival in patients with melanoma as compared with low-dose IL-2 alone.

Prevention of graft-versus-host disease by adoptive T regulatory therapy is associated with active repression of peripheral blood Toll-like receptor 5 mRNA expression

Acute graft-versus-host disease (GVHD) occurs in 40% to 60% of recipients of partially matched umbilical cord blood transplantation (UCBT). In a phase I study, adoptive transfer of expanded CD4(+)CD25(+)Foxp3(+) natural regulatory T cells (nTregs) resulted in a reduced incidence of grade II-IV acute GVHD. To investigate potential mechanisms responsible for the reduced GVHD risk, we analyzed peripheral blood mononuclear cell mRNA expression of a tolerance gene set previously identified in operation- tolerant kidney transplant recipients, comparing healthy controls and patients who received nTregs and those who did not receive nTregs with and without experiencing GVHD. Samples from patients receiving nTregs regardless of GVHD status showed increased expression of Foxp3 expression, as well as B cell-related tolerance marker. This was correlated with early B cell recovery, predominately of naïve B cells, and nearly normal T cell reconstitution. CD8(+) T cells showed reduced signs of activation (HLA-DR(+) expression) compared with conventionally treated patients developing GVHD. In contrast, patients with GVHD had significantly increased TLR5 mRNA expression, whereas nTreg-treated patients without GVHD had reduced TLR5 mRNA expression. We identified Lin(-)HLADR(-)CD33(+)CD16(+) cells and CD14(++)CD16(-) monocytes as the main TLR5 producers, especially in samples of conventionally treated patients developing GVHD. Taken together, these data reveal interesting similarities and differences between tolerant organ and nTreg-treated hematopoietic stem cell transplantation recipients.

The autoimmunity-associated gene PTPN22 potentiates toll-like receptor-driven, type 1 interferon-dependent immunity

Immune cells sense microbial products through Toll-like receptors (TLR), which trigger host defense responses including type 1 interferons (IFNs) secretion. A coding polymorphism in the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene is a susceptibility allele for human autoimmune and infectious disease. We report that Ptpn22 selectively regulated type 1 IFN production after TLR engagement in myeloid cells. Ptpn22 promoted host antiviral responses and was critical for TLR agonist-induced, type 1 IFN-dependent suppression of inflammation in colitis and arthritis. PTPN22 directly associated with TNF receptor-associated factor 3 (TRAF3) and promotes TRAF3 lysine 63-linked ubiquitination. The disease-associated PTPN22W variant failed to promote TRAF3 ubiquitination, type 1 IFN upregulation, and type 1 IFN-dependent suppression of arthritis. The findings establish a candidate innate immune mechanism of action for a human autoimmunity "risk" gene in the regulation of host defense and inflammation.

Autocrine IFN-γ promotes naive CD8 T cell differentiation and synergizes with IFN-α to stimulate strong function

Autocrine IFN-γ signaling is important for CD4 differentiation to Th1 effector cells, but it has been unclear whether it contributes to CD8 T cell differentiation. We show in this paper that naive murine CD8 T cells rapidly and transiently produce low levels of IFN-γ upon stimulation with Ag and B7-1, with production peaking at ∼8 h and declining by 24 h. The autocrine IFN-γ signals for upregulation of expression of T-bet and granzyme B and induces weak cytolytic activity and effector IFN-γ production. IFN-α acts synergistically with IFN-γ to support development of strong effector functions, whereas IL-12 induces high T-bet expression and strong function in the absence of IFN-γ signaling. Thus, IFN-γ is not only an important CD8 T cell effector cytokine, it is an autocrine/paracrine factor whose contributions to differentiation vary depending on whether the response is supported by IL-12 or type I IFN.

Inflammatory cytokines as a third signal for T cell activation

CD8 T cells require a third signal, along with Ag and costimulation, to make a productive response and avoid death and/or tolerance induction. Recent studies indicate that IL-12 and Type I IFN (IFNalpha/beta) are the major sources of signal 3 in a variety of responses, and that the two cytokines stimulate a common regulatory program involving altered expression of about 350 genes. Signal 3-driven chromatin remodeling is likely to play a major role in this regulation. Although less well studied, there is emerging evidence that CD4 T cells may also require a 'third signal' for a productive response and that IL-1 can provide this signal. Signal 3 cytokines can replace adjuvants in supporting in vivo T cell responses to peptide and protein antigens, and a better understanding of their activities and mechanisms should contribute to more rational design of vaccines.

Gene regulation and chromatin remodeling by IL-12 and type I IFN in programming for CD8 T cell effector function and memory

A third signal that can be provided by IL-12 or type I IFN is required for differentiation of naive CD8 T cells responding to Ag and costimulation. The cytokines program development of function and memory within 3 days of initial stimulation, and we show here that programming involves regulation of a common set of approximately 355 genes including T-bet and eomesodermin. Much of the gene regulation program is initiated in response to Ag and costimulation within 24 h but is then extinguished unless a cytokine signal is available. Histone deacetylase inhibitors mimic the effects of IL-12 or type I IFN signaling, indicating that the cytokines relieve repression and allow continued gene expression by promoting increased histone acetylation. In support of this, increased association of acetylated histones with the promoter loci of granzyme B and eomesodermin is shown to occur in response to IL-12, IFN-alpha, or histone deacetylase inhibitors. Thus, IL-12 and IFN-alpha/beta enforce in common a complex gene regulation program that involves, at least in part, chromatin remodeling to allow sustained expression of a large number of genes critical for CD8 T cell function and memory.

Programming for CD8 T cell memory development requires IL-12 or type I IFN

Inflammation can have both positive and negative effects on development of CD8 T cell memory, but the relative contributions and cellular targets of the cytokines involved are unclear. Using CD8 T cells lacking receptors for IL-12, type I IFN, or both, we show that these cytokines act directly on CD8 T cells to support memory formation in response to vaccinia virus and Listeria monocytogenes infections. Development of memory to vaccinia is supported predominantly by IL-12, whereas both IL-12 and type I IFN contribute to memory formation in response to Listeria. In contrast to memory formation, the inability to respond to IL-12 or type I IFN had a relatively small impact on the level of primary expansion, with at most a 3-fold reduction in the case of responses to Listeria. We further show that programming for memory development by IL-12 is complete within 3 days of the initial naive CD8 T cell response to Ag. This programming does not result in formation of a population that expresses killer cell lectin-like receptor G1, and the majority of the resulting memory cells have a CD62L(high) phenotype characteristic of central memory cells. Consistent with this, the cells undergo strong expansion upon rechallenge and provide protective immunity. These data demonstrate that IL-12 and type I IFN play an essential early role in determining whether Ag encounter by naive CD8 T cells results in formation of a protective memory population.

Signal 3 availability limits the CD8 T cell response to a solid tumor

CD8 T cells need a third signal, along with Ag and costimulation, for effective survival and development of effector functions, and this can be provided by IL-12 or type I IFN. Adoptively transferred OT-I T cells, specific for H-2K(b) and OVA, encounter Ag in the draining lymph nodes of mice with the OVA-expressing E.G7 tumor growing at a s.c. site. The OT-I cells respond by undergoing limited clonal expansion and development of effector functions (granzyme B expression and IFN-gamma production), and they migrate to the tumor where they persist but fail to control tumor growth. In contrast, OT-I T cells deficient for both the IL-12 and type I IFN receptors expand only transiently and rapidly disappear. These results suggested that some signal 3 cytokine is available, but that it is insufficient to support a CTL response that can control tumor growth. Consistent with this, administration of IL-12 at day 10 of tumor growth resulted in a large and sustained expansion of wild-type OT-I cells with enhanced effector functions, and tumor growth was controlled. This did not occur when the OT-I cells lacked the IL-12 and type I IFN receptors, demonstrating that the therapeutic effect of IL-12 results from direct delivery of signal 3 to the CD8 T cells responding to tumor Ag in the signal 3-deficient environment of the tumor.

Activation-induced non-responsiveness (anergy) limits CD8 T cell responses to tumors

Naïve CD8 T cells respond to signals provided by Ag, costimulation and cytokines by proliferating and differentiating to develop effector functions. Following initial clonal expansion, however, the cells develop activation-induced non-responsiveness (AINR), a form of anergy characterized by an inability to produce IL-2. Cells in the AINR state can carry out effector functions (cytolysis, IFN-gamma production) but cannot continue to proliferate and expand in the face of persisting Ag. AINR limits the ability of activated CTL to control tumor growth but can be reversed by IL-2, provided either therapeutically or by activated CD4 T helper cells, to allow continued expansion.

The CD8 T cell response to vaccinia virus exhibits site-dependent heterogeneity of functional responses

CD8 T cell responses to vaccinia virus (VV) and a virus-encoded ovalbumin peptide (OVAP) epitope were examined using adoptively transferred OT-I T cells. The results demonstrate that upon intra-peritoneal challenge with ovalbumin-expressing VV (VV-OVAP), OT-I T cell proliferation occurs initially in lymph nodes and spleens followed by migration of the divided cells to the peritoneal cavity. Massive clonal expansion occurs in response to both the virus and the virus-encoded ovalbumin (OVA) epitope, as demonstrated using low numbers of adoptively transferred cells, and the responding OT-I cells display marked site-dependent functional heterogeneity with respect to IFN-gamma and tumor necrosis factor-alpha (TNF-alpha) production and granzyme B expression. OT-I cells responding to VV-OVAP develop the capacity to produce IFN-gamma in response to antigen as they proliferate and differentiate. In marked contrast, naive OT-I cells rapidly produce TNF-alpha upon antigen recognition, and this capacity declines as the cells proliferate in response to the virus, suggesting that this potent inflammatory cytokine may be important primarily during initiation of the response. At the peak of clonal expansion, a large fraction (30-60%) of the OT-I cells responding to the virus express high IL-7Ralpha levels, and the majority of these cells is subsequently lost. While high IL-7Ralpha expression may be necessary for a CD8 T cell to transition to memory, it is clearly not sufficient. Thus, OT-I cells responding to VV infection exhibit a high degree of heterogeneity within the responding population that differs depending on their anatomical location, despite the specificity and affinity of the TCR being identical on all of the cells.

Molecular basis for checkpoints in the CD8 T cell response: tolerance versus activation

CD8 T cells specific for self-antigens are present in the peripheral lymphoid system and can contribute to autoimmunity or transplant rejection. Whether recognition of Ag leads to full activation, or to induction of tolerance, depends upon availability of cytokine at critical stages of the response. Signals provided by IL-12 and/or IFN-alpha/beta are required for activation of naïve CD8 T cells, and IL-2 is needed to sustain and further expand the effector cells if Ag persists. These critical signaling requirements provide new insights into the factors that regulate the CD8 T cell contributions to development of autoimmunity or rejection of transplants.

Signals required for programming effector and memory development by CD8+ T cells

Stimulation of naïve CD8+ T cells with antigen and costimulation results in proliferation and weak clonal expansion, but the cells fail to develop effector functions and are tolerant long term. Initiation of the program leading to the strong expansion and development of effector functions and memory requires a third signal that can be provided by interleukin-12 (IL-12) or interferon-alpha (IFN-alpha). CD4+ T cells condition dendritic cells (DCs) to effectively present antigen to CD8+ T cells, and this conditioning involves, at least in part, CD40-dependent upregulation of the production of these signal 3 cytokines by the DCs. Upon being fully activated, the cytotoxic T lymphocytes develop activation-induced non-responsiveness (AINR), a form of split anergy characterized by an inability to produce IL-2 to support continued expansion. If antigen remains present, IL-2 provided by CD4+ T cells can reverse AINR to allow further expansion of the effector population and conversion to responsive memory cells following antigen clearance. If IL-2 or potentially other proliferative signals are not available, persistent antigen holds cells in the AINR state and prevents the development of a responsive memory population. Thus, in addition to antigen and costimulation, CD8+ T cells require cytokine signals at distinct stages of the response to be programmed for optimal generation of effector and memory populations.

Signal 3 tolerant CD8 T cells degranulate in response to antigen but lack granzyme B to mediate cytolysis

Naive CD8 T cells that respond in vivo to Ag and costimulation in the absence of a third signal, such as IL-12, fail to develop cytolytic function and become tolerized. We show in this study that CD8 T cells purified from TCR transgenic mice and stimulated in vitro in the presence or absence of IL-12 form conjugates with specific target cells, increase intracellular Ca2+, and undergo degranulation to comparable extents. Perforin is also expressed at comparable levels in the absence or presence of a third signal, but expression of granzyme B depends upon IL-12. Levels of granzyme B also correlate strongly with the cytolytic activity of cells responding in vivo. In contrast, an increase in CD107a (lysosomal-associated membrane protein 1) expression resulting from degranulation cannot distinguish in vivo generated lytic effector cells from tolerized, noncytolytic cells. Thus, it appears that cells rendered tolerant as a result of stimulation in the absence of a third signal fail to lyse target cells because they are "shooting blanks."

CD4 T cell-dependent conditioning of dendritic cells to produce IL-12 results in CD8-mediated graft rejection and avoidance of tolerance

Rejection of ectopic heart transplants expressing OVA requires OVA-specific CD4 and CD8 T cells. In the absence of CD4 T cells, OVA-specific CD8 T cells proliferate and migrate to the graft, but fail to develop cytolytic functions. With CD4 T cells present, clonal expansion of the CD8 T cells is only marginally increased but the cells now develop effector functions and mediate rapid graft rejection. In the presence of CD4 T cells, Ag and B7 levels do not increase on dendritic cells but IL-12 production is up-regulated, and this requires CD154 expression on the CD4 T cells. OVA-specific CD8 T cells lacking the IL-12 receptor fail to differentiate or mediate graft rejection even when CD4 T cells are present. Thus, CD4 T cells condition dendritic cells by inducing the production of IL-12, which is needed as the "third signal" for CD8 T cell differentiation and avoidance of tolerance.

Cutting Edge: Type I IFNs Provide a Third Signal to CD8 T Cells to Stimulate Clonal Expansion and Differentiation

In this study, we show that IFN-alpha beta can have a direct role in linking innate and adaptive responses by providing the "third signal" needed by naive CD8 T cells responding to Ag and costimulatory ligands. Stimulation of CD8 T cells in the absence of a third signal leads to proliferation, but clonal expansion is limited by poor survival and effector functions do not develop. We show that IFN-alpha beta can provide the third signal directly to CD8 T cells via a STAT4-dependent pathway to stimulate survival, development of cytolytic function, and production of IFN-gamma. Provision of the third signal by either IFN-alpha beta or IL-12 results in regulation of the expression of a number of genes, including several that encode proteins critical for effector function.

CD8 T cell clonal expansion and development of effector function require prolonged exposure to antigen, costimulation, and signal 3 cytokine

Full activation of naive CD8 T cells requires Ag, costimulation, and a third signal that can be provided by IL-12. Brief exposure (6 h) to Ag and B7-1 is sufficient to stimulate multiple rounds of cell division, but clonal expansion and development of effector function are minimal even when signal 3 is present. Full activation instead requires concerted signaling by Ag, B7-1, and IL-12 for greater than 40 h. Thus, the gene expression program required for cell division can be initiated by brief interaction with Ag and costimulation, but maintaining the expression of the genes needed for survival and effector function requires prolonged signaling by a signal 3 cytokine in concert with Ag and costimulation.

Signal 3 determines tolerance versus full activation of naive CD8 T cells: dissociating proliferation and development of effector function

Activation of naive CD8 T cells to undergo clonal expansion and develop effector function requires three signals: (a) Ag, (b) costimulation, and (c) IL-12 or adjuvant. The requirement for the third signal to stimulate Ag-dependent proliferation is variable, making the greatest contribution when Ag levels are low. At high Ag levels, extensive proliferation can occur in vitro or in vivo in the absence of a third signal. However, despite having undergone the same number of divisions, cells that expand in the absence of a third signal fail to develop cytolytic effector function. Thus, proliferation and development of cytolytic function can be fully uncoupled. Furthermore, these cells are rendered functionally tolerant in vivo, in that subsequent restimulation with a potent stimulus results in limited clonal expansion, impaired IFN-gamma production, and no cytolytic function. Thus, the presence or absence of the third signal appears to be a critical variable in determining whether stimulation by Ag results in tolerance versus development of effector function and establishment of a responsive memory population.

The adjuvant effects of Mycobacterium tuberculosis heat shock protein 70 result from the rapid and prolonged activation of antigen-specific CD8+ T cells in vivo

Heat shock protein 70 (hsp70) is a potent adjuvant that links innate and adaptive immune responses. To study how hsp70 activates naive CD8(+) T cells in vivo, we tracked Ag-specific CD8(+) T cells in mice immunized with a fusion protein containing chicken OVA linked to hsp70 derived from Mycobacterium tuberculosis (OVA.TBhsp70). On a molar basis, OVA.TBhsp70 was several hundred times more effective than OVA peptide plus CFA in eliciting specific CD8(+) T cell responses. Immunization with OVA.TBhsp70 activated >90% of detectable OVA-specific CD8(+) T cells within 3 days and led to the persistence of cytotoxic effectors for at least 17 days. These studies demonstrate that the potent adjuvant effect of M. tuberculosis hsp70 results from the relatively complete, rapid, and durable activation of Ag-specific CD8(+) T cells.

Inflammatory cytokines provide a third signal for activation of naive CD4+ and CD8+ T cells

The effects of inflammatory cytokines on naive T cells have been studied using MHC protein/peptide complexes on microspheres, thus avoiding the use of APCs whose functions may be affected by the cytokines. IL-1, but not IL-12, increased proliferation of CD4+ T cells in response to Ag and IL-2, which is consistent with effects on in vivo priming of CD4+ cells. In contrast, proliferation of CD8+ T cells to Ag and IL-2 required IL-12, and IL-12 replaced adjuvant in stimulating an in vivo response to peptide. These results support a model in which distinct inflammatory cytokines act directly on naive CD4+ and CD8+ T cells to provide a third signal, along with Ag and IL-2, to optimally activate differentiation and clonal expansion.

Inflammatory Cytokines Provide a Third Signal for Activation of Naive CD4+ and CD8+ T Cells

The effects of inflammatory cytokines on naive T cells have been studied using MHC protein/peptide complexes on microspheres, thus avoiding the use of APCs whose functions may be affected by the cytokines. IL-1, but not IL-12, increased proliferation of CD4+ T cells in response to Ag and IL-2, which is consistent with effects on in vivo priming of CD4+ cells. In contrast, proliferation of CD8+ T cells to Ag and IL-2 required IL-12, and IL-12 replaced adjuvant in stimulating an in vivo response to peptide. These results support a model in which distinct inflammatory cytokines act directly on naive CD4+ and CD8+ T cells to provide a third signal, along with Ag and IL-2, to optimally activate differentiation and clonal expansion.

CD8+ memory T cells (CD44high, Ly-6C+) are more sensitive than naive cells to (CD44low, Ly-6C-) to TCR/CD8 signaling in response to antigen

Memory CD8+ T cells from mice previously primed with alloantigen (alloAg) can respond in vitro to IL-2 and purified class I alloAg presented on microspheres, while no response can be detected using cells from naive mice. Similar results have been obtained using cells from OT-1 mice expressing a transgenic TCR that is specific for OVA(257-264) (SIINFEKL) peptide bound to H-2Kb. A population of resting memory cells (defined on the basis of low forward scatter and CD44high, Ly-6C+, CD25-, CD69-surface phenotype) that is present in the OT-1 mice exhibits a substantially higher sensitivity to Ag-stimulation than do naive cells (CD44low, Ly-6C-) expressing the same TCR. CD44high cells respond vigorously to H-2Kb immobilized on microspheres and pulsed with peptide, while CD44low cells respond weakly and only at high class I density and peptide concentration. The Ag-presenting surface only has ligands for TCR and CD8 (class I and peptide), thus ruling out the possibility that differences are due to ligand binding by other adhesion or costimulatory receptors that are expressed at high levels on the memory cells. Experiments using anti-TCR mAb as the stimulus and coimmobilized non-Ag class I as a ligand for CD8 suggest that the difference between naive and memory cells may be at the level of stimulation through the TCR. Thus, in addition to expressing increased levels of adhesion receptors that may enhance responses to Ag on APCs, memory CD8+ T cells appear to be intrinsically more sensitive than naive cells to stimulation through the TCR/CD8 complex.

CD8+ Memory T Cells (CD44high, Ly-6C+) Are More Sensitive than Naive Cells (CD44low, Ly-6C−) to TCR/CD8 Signaling in Response to Antigen

Memory CD8+ T cells from mice previously primed with alloantigen (alloAg) can respond in vitro to IL-2 and purified class I alloAg presented on microspheres, while no response can be detected using cells from naive mice. Similar results have been obtained using cells from OT-1 mice expressing a transgenic TCR that is specific for OVA257–264 (SIINFEKL) peptide bound to H-2Kb. A population of resting memory cells (defined on the basis of low forward scatter and CD44high, Ly-6C+, CD25−, CD69− surface phenotype) that is present in the OT-1 mice exhibits a substantially higher sensitivity to Ag-stimulation than do naive cells (CD44low, Ly-6C−) expressing the same TCR. CD44high cells respond vigorously to H-2Kb immobilized on microspheres and pulsed with peptide, while CD44low cells respond weakly and only at high class I density and peptide concentration. The Ag-presenting surface only has ligands for TCR and CD8 (class I and peptide), thus ruling out the possibility that differences are due to ligand binding by other adhesion or costimulatory receptors that are expressed at high levels on the memory cells. Experiments using anti-TCR mAb as the stimulus and coimmobilized non-Ag class I as a ligand for CD8 suggest that the difference between naive and memory cells may be at the level of stimulation through the TCR. Thus, in addition to expressing increased levels of adhesion receptors that may enhance responses to Ag on APCs, memory CD8+ T cells appear to be intrinsically more sensitive than naive cells to stimulation through the TCR/CD8 complex.

Molecular analysis of the immune response to human cytomegalovirus glycoprotein B (gB). II. Low gB-specific T and B cell responses are associated with expression of certain HLA-DR alleles

Human cytomegalovirus (HCMV) is a common cause of congenital infection leading to birth defects and a leading cause of serious illness in patients with immunodeficiencies. Studies in this laboratory have focused on a molecular analysis of the immune response to glycoprotein B (gB) of HCMV. This protein has been shown to elicit B cell, helper T cell (Th), and cytotoxic T cell responses, suggesting that it may be useful as a subunit HCMV vaccine. However, previous studies showed that although peripheral blood mononuclear cells (PBMC) from all HCMV-seropositive donors proliferate in response to stimulation with whole HCMV, not all donors respond to purified recombinant gB. In the present study, PBMC from HCMV-seropositive donors homozygous for HLA-DR were tested for proliferative responses to whole HCMV and to purified gB expressed in vaccinia virus. PBMC from all donors proliferated in response to HCMV, but those from multiple donors expressing the HLA-DR3Dw3 and -DR4Dw4 specificities, and single donors expressing the -DR15Dw2, -DR13Dw19 and -DR14Dw9 specificities, failed to respond to gB. These results suggested a possible HLA-DR association with low proliferative responses to gB. In further studies, PBMC from donors expressing both putative gB-high responder and low responder HLA-DR alleles were stimulated multiple times with gB to generate gB-specific T cell lines. These cells were then tested for proliferative responses to gB presented by irradiated PBMC sharing only one DR allele with the responder cells. Cells from the gB-specific lines proliferated only when antigen was presented in the context of a responder DR allele but not when presented in the context of a low responder DR allele. Analysis of immune sera revealed that those from donors with PBMC proliferative responses always contained antibodies reactive with B cell epitopes on both the N-terminal gp93 and C-terminal gp55 portions of gB. In contrast, many of the sera from donors with low gB-specific proliferative responses had gp55-specific antibodies but lacked antibodies to gp93. These results suggest that immunogenetic differences in Th responsiveness to gB may lead to lack of antigen-specific help for antibody responses to gp93 in some cases. The prevalence of these low responder HLA alleles in the population, and the central importance of the T cell response to the generation of antibodies suggest that native gB alone may not be an attractive candidate for an HCMV subunit vaccine.

DQ beta sequences in HLA-DR4 haplotypes

A cDNA clone encoding the entire mature DQ beta chain was isolated and sequenced from the DR4-Dw14 homozygous cell line, LS40. The sequence was compared with published DQ beta sequences from cells expressing DR4-DQw3, and found to be identical. The lack of DQ beta sequence polymorphism within this serotype (to date, DQ beta sequences have been derived from five cell lines comprising three Dw subtypes) adds to the data that suggest a recent evolutionary divergence of Dw subtypes within DR4-DQw3.

Evolutionary and genetic implications of sequence variation in two nonallelic HLA-DR beta-chain cDNA sequences

Most HLA haplotypes carry two expressed DR beta-chain genes; in the DR4 haplotype, the polymorphic locus has been called DR beta 1 and the apparently nonpolymorphic locus has been called DR beta 2. We have isolated nearly full-length DR beta-chain cDNA clones representing each of these two loci from a cell line homozygous for DR4 and Dw4. The clones have been sequenced and the sequences compared with published DR beta cDNA sequences derived from other haplotypes. A comparison of our sequences with other published cDNA sequences did not allow assignment of these other sequences to either the beta 1 or beta 2 locus. Comparison of our DR4 beta 1 sequence with DR beta 1 sequences isolated from other DR4-positive cells suggests that the alleles of DR4 beta 1 may have recently diverged from a common ancestor. The apparent lack of polymorphism of DR beta 2 may in part be a reflection of this recent divergence.

Sequence polymorphism of HLA DR beta 1 alleles relating to T-cell-recognized determinants

HLA class II molecules are a highly polymorphic family of dimeric cell-surface proteins primarily involved in regulating T-cell responses to extrinsic antigens. To define regions of class II molecules involved in T-cell recognition, we have now compared sequences of three HLA DR beta cDNA clones obtained from cells that all express the same serologically defined determinants but differ in terms of T-cell-recognized specificities. The comparisons indicate that very few (one to four) nucleotides differ between what are almost certainly alleles of the DR beta 1 locus. All differences were in the first domain of the molecule and all localized to a region from amino acids 71-86. Because all differences were found only in this region of the molecule, and because DR alpha-chains seem to be relatively non-polymorphic, these positions in the DR beta-chain must have a major role in influencing T-cell recognition of the DR molecule.

A helper factor needed for the generation of mouse cytolytic T lymphocytes is made by tumor cell lines, cloned T cells, and spleen cells exposed to a variety of stimuli

A helper factor termed cytolytic T lymphocyte helper factor (CHF) that is needed for the generation of allospecific mouse cytolytic T lymphocytes (CTL) in vitro was produced by mouse spleen cells 3 to 4 days after the time when interleukin 2 (IL 2) had reached its maximal production. These kinetics were observed by stimulation of immune spleen cells with allogeneic tumor or spleen cells, with Sendai or influenza viral peptides, with virus infected cells, or with concanavalin A (Con A). CHF produced by rat spleen cells was able to help in the generation of mouse CTL, indicating that this cytokine was not restricted genetically. CHF could also be made by WEHI-3 and EL4 cell lines, as well as cloned cytolytic and helper T cells. The production of CHF by WEHI-3 cells argues that CHF is not IL 2. In addition, if CHF was not present early in the in vitro stimulation no CTL were generated, suggesting that CHF participated in the activation of CTL precursors. The addition of IL 2-containing conditioned medium to the CHF assay resulted in no substantial CTL generation, although significant cellular proliferation was observed. In contrast, CHF-containing conditioned medium allowed the generation of CTL in the absence of the same level of proliferation.

Interleukin 3 augments the murine primary cytolytic T lymphocyte response to allogeneic tumor cells

The primary anti-H-2k allospecific cytolytic T lymphocyte (CTL) response by BALB/c (H-2d) spleen cells in vitro to x-irradiated RDM4 (H-2k) tumor cells is weak. This response has been shown to be augmented by CTL helper factor (CHF), a factor present in supernatants of spleen cells cultured with Sendai virus (SC-CM). Conditioned medium from WEHI-3 cells (WEHI-CM) also contains activity that augments the BALB/c anti- RDM4 CTL response. Attempts to separate the CHF activity from interleukin 3 (IL 3), also present in WEHI-CM, were unsuccessful. Purified IL 3 was then tested, and was found to increase the BALB/c anti- RDM4 CTL response by five- to 10-fold. IL 3 is apparently the only material in WEHI-CM that is active in this assay. The response is apparently a classical CTL response because: 1) the effector cells are sensitive to monoclonal anti-Thy-1.2 antibody plus C; 2) the response is dependent on antigen stimulation, and it peaks on day 5 or 6 of culture; and 3) the effector cells are specific for H-2k targets. IL 3 must be added very early during the in vitro culture period for maximal augmentation of the response, consistent with possible action of IL 3 as a differentiation factor.

Interleukin 3 augments the murine primary cytolytic T lymphocyte response to allogeneic tumor cells

The primary anti-H-2k allospecific cytolytic T lymphocyte (CTL) response by BALB/c (H-2d) spleen cells in vitro to x-irradiated RDM4 (H-2k) tumor cells is weak. This response has been shown to be augmented by CTL helper factor (CHF), a factor present in supernatants of spleen cells cultured with Sendai virus (SC-CM). Conditioned medium from WEHI-3 cells (WEHI-CM) also contains activity that augments the BALB/c anti- RDM4 CTL response. Attempts to separate the CHF activity from interleukin 3 (IL 3), also present in WEHI-CM, were unsuccessful. Purified IL 3 was then tested, and was found to increase the BALB/c anti- RDM4 CTL response by five- to 10-fold. IL 3 is apparently the only material in WEHI-CM that is active in this assay. The response is apparently a classical CTL response because: 1) the effector cells are sensitive to monoclonal anti-Thy-1.2 antibody plus C; 2) the response is dependent on antigen stimulation, and it peaks on day 5 or 6 of culture; and 3) the effector cells are specific for H-2k targets. IL 3 must be added very early during the in vitro culture period for maximal augmentation of the response, consistent with possible action of IL 3 as a differentiation factor.

A helper factor needed for the generation of mouse cytolytic T lymphocytes is made by tumor cell lines, cloned T cells, and spleen cells exposed to a variety of stimuli

A helper factor termed cytolytic T lymphocyte helper factor (CHF) that is needed for the generation of allospecific mouse cytolytic T lymphocytes (CTL) in vitro was produced by mouse spleen cells 3 to 4 days after the time when interleukin 2 (IL 2) had reached its maximal production. These kinetics were observed by stimulation of immune spleen cells with allogeneic tumor or spleen cells, with Sendai or influenza viral peptides, with virus infected cells, or with concanavalin A (Con A). CHF produced by rat spleen cells was able to help in the generation of mouse CTL, indicating that this cytokine was not restricted genetically. CHF could also be made by WEHI-3 and EL4 cell lines, as well as cloned cytolytic and helper T cells. The production of CHF by WEHI-3 cells argues that CHF is not IL 2. In addition, if CHF was not present early in the in vitro stimulation no CTL were generated, suggesting that CHF participated in the activation of CTL precursors. The addition of IL 2-containing conditioned medium to the CHF assay resulted in no substantial CTL generation, although significant cellular proliferation was observed. In contrast, CHF-containing conditioned medium allowed the generation of CTL in the absence of the same level of proliferation.