Abstract 1769: Loss of major histocompatibility class II expression in diffuse large B-cell lymphoma may be related to stage of B-cell differentiation

Abstract

Abstract Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma diagnosed in the U.S. It displays marked heterogeneity, biologically and clinically, with patients demonstrating a wide range of responses to therapy. Major histocompatibility class II (MHCII) molecules are involved in antigen presentation and are vital to the immune system. Decreased MHCII expression is one of the normal changes seen as B-cells differentiate into mature, antibody-secreting plasma cells. This decrease occurs in concert with changes in other proteins and transcription factors which define the phenotype of a B- or plasma cell. Loss of MHCII expression in DLBCL patients is associated with extremely poor prognosis. In this study, we asked whether MHCII loss in DLBCL was associated with a more differentiated phenotype. We hypothesized that malignant cells from MHCII(-) DLBCL cases would be closer to the plasma cell end of the differentiation spectrum than MHCII(+) cases. We previously used a 40-case tissue microarray to demonstrate that although MHCII(-) DLBCL cases did not present a fully plasma cell differentiated phenotype, protein expression of the late B-cell marker, MUM1/IRF4, was inversely associated with MHCII, suggesting that MHCII loss may be associated with cases further along the differentiation continuum (Wilkinson, AACR 2009). Here, we built upon this work using immunohistochemistry (IHC) to score expression of a panel of B- and plasma cell markers. These included B-cell transcription factors Oct2, Bob 1, Pax5 and mature B-cell surface marker CD20 as well as plasma cell markers XBP1, BLIMP1, and CD138. IHC results were semi-quantitatively assessed by scoring both frequency and intensity of staining. The results were compared to MHCII expression as previously determined with gene expression profiling and IHC. Using this routine IHC assessment, the presence of plasma cell markers XBP1, BLIMP1, or CD138 did not correlate with low or absent expression of MHCII, while the B-cell markers were present in most cases. Thus, no clear evidence of a more differentiated phenotype was observed in MHCII(-) DLBCL. These findings could result from lack of association between loss of MHCII expression and plasma cell differentiation or the limitations of the methodology used. To further investigate this question, we have developed protocols with QdotsR (Life Technologies) to more accurately quantify expression of the plasma cell-associated proteins relative to MHCII. By using nanocrystals with narrow emission spectra coupled to monoclonal antibodies, multiple colors can be visualized and specifically measured in each cell. This technique may yield more accurate, quantitative data regarding protein expression of plasma cell markers and MHCII. The results of these studies should lead to a better understanding of MHCII expression in DLBCL with possible implications for therapeutic targeting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1769.