Mechanisms of humoral immune dysfunction in CLL

• Applicants: Dr. Gero Knittel, Ph.D.; Professor Dr. Ralf Küppers
• Subject Area: Hematology, Oncology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512340830

Chronic lymphocytic leukemia (CLL) is the most common leukemia among elderly humans and is still incurable. Progressive immunodeficiency is a hallmark of CLL, and infections are one of the most common causes of death for CLL patients. An important, but poorly understood cause of this immune dysfunction is an impaired B-cell system. CLL patients have two discrete types of B cells, the malignant CLL clone, and the residual normal B-cell compartment. Through various interactions, the nonmalignant B cells are also affected by the CLL. We aim to elucidate the mechanisms by which CLL causes humoral immunodeficiency and thereby sharply increases the risk of life-threatening infections: Aim 1) Reveal the disturbed normal B-cell subset composition and B-cell receptor (BCR) repertoire of CLL patients and its contribution to impaired humoral immunity. Are similar phenomena recapitulated in the well-accepted Eμ-TCL1 CLL mouse model? Aim 2) Determine to what extent and through which mechanisms CLL cells impair the activation potential and terminal differentiation of normal B cells in patients and E-TCL1 mice. Aim 3) Determine how CLL cells impair T cell–dependent immune responses of normal B cells and thereby the generation of high-affinity memory B cells and plasma cells. Study humoral immune responses against S. pneumoniae infection under the influence of CLL in the Eμ-TCL1 mouse model, with a focus on mechanistic alterations in the germinal center reaction. Aim 4) Clarify whether bone marrow-infiltrating CLL cells cause the replacement of long-lived normal plasma cells from their survival niches and thereby cause hypogammaglobulinemia.For aim 1, we will phenotype non-CLL B cells in peripheral blood from CLL patients and Eμ-TCL1 mice and determine their BCR repertoire by deep sequencing. For aim 2, we will perform in vitro coculture studies of CLL and non-CLL B cells and compare the in vitro response to various stimuli of normal B cells from CLL patients and healthy donors, and similarly for Eμ-TCL1 mice. Functional in vitro assays shall reveal deregulated gene expression and antibacterial responses in normal B cells from CLL patients. For aim 3, we will immunize or infect CLL-bearing mice and study the germinal center response, the generation of memory and plasma cells, the course of bacterial infections, and the reactivation potential of memory B cells. For aim 4, we plan microscopic and flow cytometric studies of plasma cells in the bone marrow of immunized and bacterially-infected CLL-bearing Eμ-TCL1 mice. Overall, using a comprehensive approach to study the main steps of B-cell differentiation and the function of untransformed B cells under the influence of CLL, we will identify the factors causing enhanced susceptibility to infections among CLL patients. It is our long-term goal to translate our findings to protect normal B cells from negative influences mediated by the CLL, thereby attenuating immunosuppression and preventing infectious diseases.

• DFG Programme: Research Grants