Natural T cell autoreactivity to melanoma antigens: clonally expanded melanoma-antigen specific CD8 + memory T cells can be detected in healthy humans

Abstract

We used four-color ImmunoSpot® assays, in conjunction with peptide pools that cover the sequence of tyrosinase (Tyr), melanoma-associated antigen A3 (MAGE-A3), melanocyte antigen/melanoma antigen recognized by T cells 1 (Melan-A/ MART-1), glycoprotein 100 (gp100), and New York esophageal squamous cell carcinoma-1 (NY-ESO-1) to characterize the melanoma antigen (MA)-specific CD8 + cell repertoire in PBMC of 40 healthy human donors (HD). Tyr triggered interferon gamma (IFN-γ)-secreting CD8 + T cells in 25% of HD within 24 h of antigen stimulation ex vivo. MAGE-A3, Melan-A/MART-1, and gp100 also induced recall responses in 10%, 7.5%, and 2.5% of HD, respectively. At this time point, these CD8 + T cells did not yet produce GzB (granzyme B). However, they engaged in GzB production after 72 h of antigen stimulation. By this 72-h time point, 57.5% of the HD responded to at least one, and typically several, of the MA. A closer characterization of the Tyr-specific CD8 + T cell repertoire indicated that it was low-affinity, and to primarily entail a stem cell-like subpopulation. Collectively, our data reveal pre-existing endogenous T cell immunity against melanoma antigens in healthy donors, and analogous to natural autoantibodies, we have termed this "natural T cell autoreactivity".

Evaluation of T-Cell Responses Against Shared Melanoma Associated Antigens and Predicted Neoantigens in Cutaneous Melanoma Patients Treated With the CSF-470 Allogeneic Cell Vaccine Plus BCG and GM-CSF

“…TAAs like PMEL/gp100, tyrosinase, and several CT Ags have been identified as melanoma regression Ags (33,34). The roles of non-mutated TAAs were recently reinvigorated as key players in the endogenous anti-melanoma immunity (35,36) since they may be involved in either CM surveillance or dormancy. In our study, vaccination with the allogeneic CSF-470 vaccine has provided sustained targeting of TAAs.…”

Functional T Cell Reactivity to Melanocyte Antigens is Lost During Development of Malignant Melanoma, but is Restored with Successful Immunotherapy

“…Relying on an ELISPOT approach that detects functional CD8+ T cells even as rare as 1:250,000 peripheral blood mononuclear cells (PBMC), and using mega peptide pools that cover all epitopes on MA, we have shown that in healthy human donors (HD) primed MA-specific CD8+ T cells can be detected [21]. Therefore, apparently not only melanoma cells are immunogenic after they have metastasized, but already regular melanocytes can trigger tumor associated antigen-specific T cell responses, and doing so without evidently harming regular melanocytes.…”

“…In analogy to natural autoantibodies [22], that also should be forbidden based on the self/non-self model, we called these CD8+ T cells natural autoreactive T cells. These MA-specific T cells recognize Tyrosinase, MAGE-A3, Melan/Mart-1, gp100, and NY-ESO-1 [21]. Reminiscent of anti-viral T cell responses [19], the T cell response against these MA is aleatory [23], i.e., it is directed against different MA in different individuals [21].…”

“…These MA-specific T cells recognize Tyrosinase, MAGE-A3, Melan/Mart-1, gp100, and NY-ESO-1 [21]. Reminiscent of anti-viral T cell responses [19], the T cell response against these MA is aleatory [23], i.e., it is directed against different MA in different individuals [21]. These MA-specific natural CD8+ T cells are in a resting memory cell stage at their isolation form the body, but within 3 days of antigen re-stimulation they become cytolytic effector cells as resting memory cells generally do.…”

“…It can be assumed that such naturally autoreactive CD8+ T cells get primed during sun burns we suffer when melanocyte activation occurs in an inflamed skin, and thus both requirements for priming of a T cell response are warranted: the temporary overexpression of the melanocyte antigens providing increased levels of TCR ligand sufficient to exceed the activation threshold of low affinity CD8 cells [24], and the "danger" environment required for the induction of immunity vs. of tolerance [25]. While such naturally autoreactive melanocyte-specific T cells might actively enhance the inflammatory response associated with the sun burn, and as such might in the long term promote melanoma development, in healthy hosts, they apparently become negligent of the autoantigen as soon as its expression level returns to normal as these cells are resting CD8 + T memory cells at their isolation [21]. But do such naturally autoreactive CD8 + T cells represent a novel line of immunity directed against melanoma?…”