Expression of tumour-specific antigens underlies cancer immunoediting

Abstract

Cancer immunoediting is a process by which immune cells, particularly lymphocytes of the adaptive immune system, protect the host from the development of cancer and alter tumour progression by driving the outgrowth of tumour cells with decreased sensitivity to immune attack. Carcinogen-induced mouse models of cancer have shown that primary tumour susceptibility is thereby enhanced in immune-compromised mice, whereas the capacity for such tumours to grow after transplantation into wild-type mice is reduced. However, many questions about the process of cancer immunoediting remain unanswered, in part because of the known antigenic complexity and heterogeneity of carcinogen-induced tumours. Here we adapted a genetically engineered, autochthonous mouse model of sarcomagenesis to investigate the process of cancer immunoediting. This system allows us to monitor the onset and growth of immunogenic and non-immunogenic tumours induced in situ that harbour identical genetic and histopathological characteristics. By comparing the development of such tumours in immune-competent mice with their development in mice with broad immunodeficiency or specific antigenic tolerance, we show that recognition of tumour-specific antigens by lymphocytes is critical for immunoediting against sarcomas. Furthermore, primary sarcomas were edited to become less immunogenic through the selective outgrowth of cells that were able to escape T lymphocyte attack. Loss of tumour antigen expression or presentation on major histocompatibility complex I was necessary and sufficient for this immunoediting process to occur. These results highlight the importance of tumour-specific-antigen expression in immune surveillance, and potentially, immunotherapy.

Figure 1. Sarcoma formation in immunodeficient mice occurs with increased penetrance and reduced latency

a and b, KPR or KP mice were injected intramuscularly with Lenti-LucOS (a) or Lenti-x (b) and the onset of palpable sarcomas was monitored. c, Time for palpable tumour formation with Lenti-LucOS or Lenti-x in KPR (circles) or KP (triangles) mice. d, Sarcoma formation in KP mice either untreated or treated with anti-CD4 and anti-CD8 antibodies beginning coincident with or 14 days after Lenti-LucOS injection. e, Sarcoma onset after injection of KP-LSIY or KP littermates with Lenti-LucS. The percentage of total mice (n) with sarcomas by 140 days (grey boxes) is indicated.

Figure 2. Functional T cell responses are generated against antigens expressed in sarcomas

a, Top: Percent of CD8⁺ cells specific for SIY- and SIN in the inguinal lymph nodes either draining (DLN) or peripheral to (PLN) Lenti-x or Lenti-LucOS tumours. Bottom: IFN-γ and TNF-α cytokine production in SIY+SIN-stimulated CD8⁺ T cells from mice analyzed above. b, Analysis of splenocytes as in (a). c and d, Cumulative data depicting the percentage of SIY and SIN-specific T cells that were IFN-γ⁺ TNF-α⁺ from lymph nodes (c) or spleens (d) of KP mice infected with Lenti-LucOS that developed a “sarcoma” or were “tumour-free” at 170 days. T cells reactive to SIY were analyzed four months after challenge with WSN-SIY (influenza strain expressing SIY). Data represents analysis of 3–4 mice per group, mean ± s.e.m.

Figure 3. Cancer immunoediting phenotypes require the presence of potent T cell antigens

Transplanted tumour growth of Lenti-LucOS-induced sarcomas generated in KPR (a) or KP (b) mice and Lenti-x-induced sarcomas generated in KPR (c) or KP (d) mice. At left, representative tumour growth curves from two different primary tumours (colored red or blue) after transplantation into Rag-2^null (dashed lines) or wild-type (WT, solid lines) mice. At right, comparison of the mean tumour volume (mm³) ± s.e.m. for all tumours transplanted. Φ indicates no detectable mass. See Supplementary Fig. 2 for growth curves of tumour lines.

Figure 4. Immunoediting occurs by selecting for tumour cells that do not express targeted antigens

a, Representative luciferase activity of Lenti-LucOS and Lenti-x-induced sarcomas in KPR, KP or anti-CD4/CD8 treated KP mice. b, Luciferase expression in Lenti-LucOS-induced sarcoma cell lines derived in KPR or KP mice. c, Freshly harvested sarcomas cultured with IFN-γ (solid line) or untreated (dashed line) were analyzed for H-2K^b surface expression (shaded, control antibody). d, Growth of two independent tumours (3919 and 4070) that had lost antigen expression (Ag^Loss, blue lines) or the same tumour lines after reintroduction of LucOS (Ag^Loss-LucOS, red lines). Mean tumour volume ± s.e.m. after transplantation into three wild-type mice (solid lines) or one Rag-2^null mouse (dashed lines). e, Relative luciferase activity (compared to the primary sarcoma) ± 5-aza-2’-deoxycytidine (Aza) of Lenti-LucOS sarcomas from KPR mice (Primary, black columns) that were passaged through Rag-2^−/− (Tx->Rag^null, grey columns) or wild-type mice (Tx->Rag⁺). Mean ± s.e.m. from two experiments.