Follicular lymphoma B cells induce the conversion of conventional CD4 + T cells to T‐regulatory cells

There has been accumulating evidence that CD4 + CD25 + FoxP3 expressing regulatory T cells (Treg) are highly concentrated in tumors, thereby fostering an immune‐privileged microenvironment. Some studies have shown that T‐cell receptor (TCR) stimulation can convert conventional T cells into Treg. Follicular lymphoma (FL) B cells can enhance this Treg conversion. We investigated whether FL tumor B cells, as opposed to normal B cells, are unique in their ability to convert effector T cells into Treg. We found that tumor B cells alone, without artificial TCR stimulation, could induce conventional T cells to express FoxP3 and to acquire regulatory function. In contrast to their malignant counterpart, normal B cells did not induce Treg conversion. Treg conversion was independent of the T cell background, as T cells isolated from FL or normal peripheral blood were equally susceptible to being converted by tumor B cells. Our study provides evidence for a tumor‐specific mechanism by which FL tumor cells promote immune escape through the induction of Treg. © 2008 Wiley‐Liss, Inc.