Antigen-Specific CD8 Lytic Phenotype Induced by Sipuleucel-T in Hormone-Sensitive or Castration-Resistant Prostate Cancer and Association with Overall Survival.

Purpose: Sipuleucel-T is FDA approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC) based on the IMPACT trial showing a 4.1-month benefit in median overall survival (OS) for patients receiving sipuleucel-T versus control. Although efficacy of sipuleucel-T is well established, its mechanism remains incompletely understood.Patients and Methods: Patient samples from three sipuleucel-T trials were assessed for peripheral cellular immune responses to the immunogen PA2024 and the target antigen prostatic acid phosphatase (PAP). PAP- and PA2024-specific proliferative and cytolytic responses were characterized to delineate sipuleucel-T-induced immune responses. To quantify potential cytotoxic T lymphocyte (CTL) activity, cell-surface CD107a expression on PAP- or PA2024-specific CD8+ T cells was measured in sipuleucel-T-treated patient and healthy volunteer samples.Results: Increased PA2024-specific CD4+ (P = 0.030) and CD8+ (P = 0.052) T-cell proliferation from baseline to week 6 was observed (N = 14) post-sipuleucel-T, with greater magnitude of PA2024-specific responses compared with PAP. PAP- and PA2024-CTL activity (CD107a positivity) significantly increased at weeks 6 and 26 after sipuleucel-T treatment (P < 0.0001; N = 22). At 26 weeks post-sipuleucel-T, OS correlated with the magnitude of PAP (Pearson R, 0.52; P = 0.013) or PA2024 (Pearson R, 0.67; P = 0.0006) CTL activity. Higher PA2024-CTL activity at week 26 was significantly associated with longer OS using tertile analysis (P = 0.0005; N = 22), with PA2024 responses correlating with PAP responses at week 26 (R = 0.90; P = 1.53E-08).Conclusions: This study is the first to report PAP-specific CD8+ T-cell responses elicited by sipuleucel-T treatment. Increased and persistent potential PA2024-specific CTL activity correlated with PAP-specific CTL activity and associated with improved OS following sipuleucel-T treatment. Clin Cancer Res; 24(19); 4662-71. ©2018 AACR.

Early consequences of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on the activation and survival of antigen-specific T cells.

TCDD is a potent immunotoxicant that suppresses adaptive immunity by mechanisms that are not well defined. To gain insight at the level of the T cell, we used the DO11.10 transgenic T-cell receptor (TCR) mouse model in an adoptive transfer approach to characterize the influence of TCDD on the responsiveness of antigen-specific CD4+ T cells in vivo. Flow cytometry was used to track the response of the OVA-specific transgenic CD4+ T cells in syngeneic recipients using an antibody specific for the transgenic TCR (KJ1-26 [KJ]). Consistent with a previous report, exposure of the recipient mice to TCDD (15 microg/kg po) did not alter the initial expansion of the CD4+KJ+ T cells in the spleen following immunization with OVA but resulted in a significant decline in the number of cells present on and after day 4. The degree of decline was dependent on the dose of TCDD. On day 3 after OVA injection, a higher percentage of the CD4+KJ+ T cells in the spleens of TCDD-treated mice had down-regulated the expression of CD62L, a phenotype associated with T-cell activation. Also on day 3, an increased number of CD4+KJ+ T cells were found in the blood of TCDD-treated mice. However, as in the spleen, the number of CD4+KJ+ T cells in the blood rapidly declined on day 4. CD4+KJ+ T cells in both the spleen and blood of TCDD-treated mice failed to up-regulate CD11a, an adhesion molecule important for sustained interaction between T cells and DC whereas the up-regulation of the adhesion molecule CD49d was not altered. Based on analysis of cell division history, CD4+KJ+ T cells in vehicle-treated mice continued to divide through day 4 whereas CD4+KJ+ T cells in TCDD-treated mice showed no further division after day 3. Increased annexin V staining on CD4+KJ+ T cells in TCDD-treated mice was also observed but not until days 5 and 6. Fas-deficient CD4+KJ+ T cells were depleted from the spleen of TCDD-treated mice in a manner similar to wild-type CD4+KJ+ T cells, suggesting that Fas signaling does not play a critical role in this model. On the other hand, gene array analysis of purified CD4+KJ+ T cells on day 3 showed that the expression of several genes associated with cell survival/death were altered by TCDD. Taken together, the results are consistent with our hypothesis that TCDD provides an early but inappropriate activation signal to the antigen-specific T cells that allows, and possibly enhances, the initial activation and proliferation of the T cells, yet at the same time, interferes with the vital expression of certain adhesion/costimulatory molecules that serve to enhance the survival of the T cells. These changes result in truncated proliferation, increased T-cell death, and suppression of the adaptive immune response.

Combination therapy with Pretarget CC49 radioimmunotherapy and gemcitabine prolongs tumor doubling time in a murine xenograft model of colon cancer more effectively than either monotherapy.

Pretarget radioimmunotherapy (RIT) is a multistep strategy for cancer therapy designed to reduce nontarget organ exposure by uncoupling the tumor targeting moiety from the radioactive ligand. Using this approach, we and others have demonstrated objective responses to therapy among patients with non-Hodgkin's lymphoma, with less hematological toxicity than is typically seen at equivalent doses of conventional RIT in the same patient population. In the present study, we show that combination therapy with gemcitabine (200 mg/kg on days -1 and +1) and Pretarget RIT (400 micro Ci (90)Y-labeled DOTA-biotin on day +1) is superior to Pretarget monotherapy (400 or 800 micro Ci (90)Y) as well as to gemcitabine monotherapy in nude mice bearing established human LS174T colon cancer xenografts. For the targeting moiety, we used a murine anti-TAG-72 (CC49) single-chain Fv-streptavidin (scFvSA) fusion protein that has been shown to be safe and well-tolerated in humans. The median number of days to tumor volume doubling in the gemcitabine-only studies (200 mg/kg) was 10.4 +/- 5.5 days; in the Pretarget 400 micro Ci dose-only studies, tumor doubling time was 6.7 +/- 4.9 days; and in combination therapy studies, it was 23.9 +/- 7.2 days (P

Influence of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the antigen-presenting activity of dendritic cells.

We have previously shown that exposure of mice to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) induces activation-like changes in splenic dendritic cells (DC) in the absence of antigen challenge. Since activation of DC reduces their ability to phagocytize antigen, we examined the effects of TCDD on the ability of DC to process and present antigen to antigen-specific T cells and to internalize latex beads. Additionally, the expression of costimulatory and adhesion molecules was examined on DC from TCDD-treated mice injected with allogeneic tumor cells. The ability of DC from C57Bl/6 mice to induce proliferation of keyhole limpet hemocyanin (KLH)-specific 10.5.17 T cells and production of IL-4 was not significantly altered by TCDD exposure, either when KLH was added in vitro or when the mice were injected with KLH prior to DC isolation. In contrast, ovalbumin (OVA) presentation by DC from TCDD-treated Balb/c mice induced enhanced proliferation of OVA-specific D011.10 T cells, although the production of IL-2 and IFN-gamma was not affected. Enhanced in vivo proliferation of adoptively transferred, CFSE-labeled DO11.10 T cells was also observed in TCDD-treated Balb/c mice that were challenged with OVA. TCDD treatment modulated the expression of major histocompatibility complex (MHC) class II, CD24, ICAM-1, CD40, and LFA-1 on splenic DC from C57Bl/6 mice injected with allogeneic tumor cells; however, the effects of TCDD were identical to changes seen previously in nonimmune mice, suggesting that these effects were not antigen-dependent. Finally, TCDD treatment did not affect the ability of splenic DC to internalize latex beads administered in vivo. Taken together, these results suggest that the activation-like changes induced in DC by TCDD do not suppress the ability of DC to process and present antigen, but may enhance their ability to provide activation signals to T cells. This, in turn, may alter the survival of the T cells, the DC, or both, and might lead to dysregulation of the immune response.