Major histocompatibility complex class II-transfected tumor cells present endogenous antigen and are potent inducers of tumor-specific immunity

Abstract

We have developed an immunotherapy in which tumor cells transfected with syngeneic major histocompatibility complex (MHC) class II genes are cell-based vaccines for the treatment of established tumor and metastatic disease. If this strategy is to be used clinically, convenient methods for generating class II+ tumor cells are necessary. Interferon-gamma treatment or transduction of the class II transactivator (CIITA) gene induces class II expression but also up-regulates the class II-associated accessory molecules, invariant chain (Ii) and DM. To determine if interferon-gamma treatment and CIITA transduction are potential immunotherapies, we assessed the tumorigenicity of sarcoma cells expressing combinations of class II, Ii, and DM. Since we hypothesized that class II-transfected tumor cells not coexpressing Ii and DM present endogenously encoded tumor peptides, we have assessed the transfectants for antigen presentation activity to MHC class II-restricted antigen-specific CD4(+) T cells. Tumor challenge studies demonstrate that tumor cells expressing class II without coexpression of Ii or Ii plus DM are highly immunogenic and preferentially present endogenous antigens, while tumors coexpressing class II with Ii or Ii plus DM are not effective immunogens. Because tumor rejection correlates with expression of class II without coexpression of Ii and DM, the most efficacious vaccines will express MHC class II without coexpression of Ii and DM and will preferentially present endogenous antigen.

Figure 1

Expression of MHC class II, Ii, and HEL in SaI and SaI-transfected tumor cells. (A) SaI and SaI/A^k sarcoma cells and their transfectants were stained for MHC class II (a–f), ER-retained HEL (g–j), plasma membrane HEL (k–n), Ii (o–t), or DM (u and v). (B) Three SaI/A^k/Ii transfected sarcoma lines (Ii-6, Ii-7, Ii-9) were stained for MHC class II (a–g), ER-retained HEL (h–k), plasma membrane HEL (l–o), Ii (p–v), or DM (w–y). (C) SaI/LXSN or SaI/CIITA sarcoma cells and their transfectants were stained for MHC class II (a–g), ER-retained HEL (h–k), plasma membrane HEL (l–p), Ii (q–w), or DM (x and y). In all panels, broken lines represent specific antibody staining; solid lines represent secondary fluorescent conjugate staining without primary antibody. MHC class II (10–2.16 mAb) and plasma membrane HEL (HyHEL 7, HyHEL 10 mAbs) staining was performed on live cells; internal HEL (ER-retained) and Ii chain staining was performed on fixed cells.