Biology and Microenvironment
J. Veldman, A. van den Berg, L. Visser, A. Diepstra
University of Groningen, University Medical Center Groningen, Department of Pathology & Medical Biology, Groningen, Netherlands
Introduction: A characteristic feature of Hodgkin lymphoma (HL) is the minority of tumor cells (<1%) that are dispersed within an abundant inflammatory infiltrate. Within this infiltrate CD4+ T cells form tight rosettes around the tumor cells and provide oncogenic stimuli to the tumor cells. Interaction between normal B and T cells involves the formation of a specialized structure called the immunological synapse. The formation involves exploratory contacts guided by adhesion molecules (e.g. CD2-CD58, CD11a/CD18-CD54), followed by initiation of synapse formation by T cell receptor (TCR)-human leukocyte antigen class (HLA) II interaction and polarization of T cells mediated by actin. We hypothesize that the interaction between Hodgkin tumor cells and T cells follows a similar order of events.
Methods: An in vitro co-culture model was used of HL cell lines with peripheral blood mononuclear cells (PBMCs) from healthy donors. Hodgkin cell lines were characterized for immunological synapse components and involvement of synapse components expressed on T cells was studied after rosette formation. Results – All Hodgkin cell lines contained CD54. HLA class I, HLA class II and CD58 expression was lost in one or more of the HL cell lines. Interestingly, already after two minutes of co-culture we observed relocalization of CD2 towards the interacting interface between T cells and tumor cells, which after several hours was even more prominent. This relocalization of CD2 was not observed in co-cultures of PBMCs with CD58 negative HL cell lines. In addition, blocking of CD2 on PBMCs before co-culturing, reduced rosetting. Actin polarization occurred within minutes in a proportion of T cells and was observed in most of the T cells after several hours. Relocalization of CD11a and the TCR was only observed in some interacting cells. In HL patient tissue we observed a strong rim of CD11a and CD2 around the Hodgkin tumor cells, highlighting the importance of both molecules for tumor cell-T cell interactions. TCR relocalization appeared less strong in patient material.
Conclusions: The interaction between Hodgkin Reed-Sternberg cells and T cells occurs through structures similar to the immunological synapse based on CD2, CD11a and actin relocalization in vitro and in patient material. Interestingly, CD2 seems to be the molecule involved in the early interacting phase in HL cell lines.