The adaptor protein SLP-65 acts as a tumor suppressor that limits pre-B cell expansion.

Mice deficient in the adaptor protein SLP-65 (also known as BLNK) have reduced numbers of mature B cells, but an increased pre-B cell compartment. We show here that compared to wild-type cells, SLP-65(-/-) pre-B cells show an enhanced ex vivo proliferative capacity. This proliferation requires interleukin 7 and expression of the pre-B cell receptor (pre-BCR). In addition, SLP-65(-/-) mice have a high incidence of pre-B cell lymphoma. Reintroduction of SLP-65 into SLP-65(-/-) pre-B cells led to pre-BCR down-regulation and enhanced differentiation. Our results indicate that SLP-65 regulates a developmental program that promotes differentiation and limits pre-B cell expansion, thereby acting as a tumor suppressor.