Malignant lymphoma cells induce tolerance of T cells

Inhibitory receptors are involvedin the induction of T cell dysfunctionand exhaustion in chronic viral infectionsand in tumors. In the presentstudy, we analyzed the expressionpattern of 3 different inhibitory receptors(PD-1, Lag-3, 2B4) in a murine Bcell lymphoma model. Furthermore,we functionally characterized CD8+T cells expressing inhibitory receptorsfor cytokine production and proliferation.Expansion and secretion ofpro-inflammatory cytokines of CD8+T cells from lymphoma-bearing E-myc mice were significantly reducedcompared to the healthy controls.Similarly, expansion and effectorfunction of CD8+ TCR transgenic(p14) Tcells specific for the gp-33 antigenof lymphocytic choriomeningitisvirus (LCMV) was reduced inlymphoma-bearing E-myc mice afteractivation with LCMV. The functionalimpairment of CTL in the presenceof lymphoma was reversible aftertransfer to naive C57BL/6 recipients.In vitro co-culture experimentsrevealed that the proliferation ofanti-CD3-activated CD8+ T cellsfrom WT mice was significantly inhibitedby CD19+ lymphoma cellsfrom E-myc mice, whereas no inhibitionwas observed after co-culturewith normal B cells. Supernatants ofin vitro cultured lymphoma B cellsand blood sera from lymphoma-bearingE-myc mice significantly reducedT cell proliferation in vitro, ascompared to supernatants from normalB cells cultures or sera of healthyanimals. These experiments indicatethat the lymphoma B cells inactivateCTL by a soluble factor. Expressionanalysis of different important immunologicalcytokines revealed that themacrophage migration inhibitory factor(MIF) is selectively overexpressedin malignant B cells. This finding wasconfirmed by analyzing MIF proteinin culture supernatants and in celllysates. Therefore, lymphoma B cellsmay reduce T cell function and suppresslymphoma surveillance by secretionof MIF.