Memory T cells are uniquely resistant to melanoma-induced suppression

Abstract

We have previously observed that in vivo exposure to growing melanoma tumors fundamentally alters activated T cell homeostasis by suppressing the ability of naïve T cells to undergo antigen-driven proliferative expansion. We hypothesized that exposure of T cells in later stages of differentiation to melanoma would have similar suppressive consequences. C57BL/6 mice were inoculated with media or syngeneic B16F10 melanoma tumors 8 or 60 days after infection with lymphocytic choriomeningitis virus (LCMV), and splenic populations of LCMV-specific T cells were quantified using flow cytometry 18 days after tumor inoculation. Inoculation with melanoma on post-infection day 8 potentiated the contraction of previously activated T cells. This enhanced contraction was associated with increased apoptotic susceptibility among T cells from tumor-bearing mice. In contrast, inoculation with melanoma on post-infection day 60 did not affect the ability of previously established memory T cells to maintain themselves in stable numbers. In addition, the ability of previously established memory T cells to respond to LCMV challenge was unaffected by melanoma. Following adoptive transfer into melanoma-bearing mice, tumor-specific memory T cells were significantly more effective at controlling melanoma growth than equivalent numbers of tumor-specific effector T cells. These observations suggest that memory T cells are uniquely resistant to suppressive influences exerted by melanoma on activated T cell homeostasis; these findings may have implications for T cell–based cancer immunotherapy.

Enhanced local and systemic anti-melanoma CD8+ T cell responses after memory T cell-based adoptive immunotherapy in mice

“…Adoptive cell transfer was performed as previously described [21, 22]. Naïve CD8+ GP33-specific T cells were derived from splenocytes harvested from Ly5.1+ P14 TCR transgenic mice (C57BL/6 background with TCR specificity for GP33).…”

“…However, the specific consequences of effector versus memory T cell transfer on the intratumoral and systemic immunological milieu and on endogenous tumor-directed T cell responses have not been clearly dissected. We have previously demonstrated that in vivo exposure to melanoma impairs the transition of resting to effector T cells and enhances the apoptotic contraction of acutely activated T cells CD8+ T cells [20, 21]; in contrast, the capacity of memory T cells for homeostatic proliferation and antigen-driven reactivation are unaltered by in vivo exposure to melanoma [22]. …”

CTLA-4 Blockade Plus Adoptive T-Cell Transfer Promotes Optimal Melanoma Immunity in Mice

“…Adoptive cell transfer as performed as previously described (9). Briefly, splenocytes were harvested from Ly5.1+ B6.SJL mice 8 days after LCMV infection, then enriched for CD8 expression using magnetic bead separation columns (Miltenyi, Auburn, CA).…”

“…Lymphocytes were stained with APC-labeled MHC class I (D b ) tetramers loaded with GP33, PErCp-labeled anti-CD8, PE-labeled anti-Ly5.1, and FITC-labeled anti-CD44 antibodies. Flow cytometric analysis of splenocytes was performed on day 9 or 14 after B16GP33 tumor inoculation using methods previously described (9-12). Briefly, freshly harvested splenocytes (10 6 cells/well) were stimulated with (or, as a negative control, without) GP33 at a concentration of 0.1 μg/mL in the presence of brefeldin A and human recombinant IL-2 (10 U/well) at 37°C for 5 hours in flat-bottomed 96-well plates.…”

“…In this study, we examined the potential immunological interaction that could take place between CTLA-4 blockade and ACT strategies. Specifically, we used a murine model of melanoma ACT previously established in our laboratory (9) to test whether CTLA-4 blockade could augment the efficacy of non-lymphodepletion ACT, and to determine if any observed augmentation was due to the potentiation of exogenously-derived populations of adoptively transferred melanoma-specific CTLs, endogenous melanoma-specific T cell responses, or both.…”