Objective. CD40L restores the antigen-presenting cell (APC) function of som
e B-cell tumors and induces professional APC maturation. We therefore evalu
ated the effects of transgenic CD40L expression on the behavior and immunog
enicity of human multiple myeloma (MM) cells.
Materials and Methods. CD40L expression was induced in a CD40(+) (RPMI 8226
) and a CD40(-) (U266B1) human myeloma cell line (HMCL) by adenoviral vecto
r gene transfer. The viability and proliferative activity of control HMCL a
nd HMCL/CD40L were determined by daily trypan blue staining and methyl-H-3-
thymidine incorporation. Mixed lymphocyte reaction (MLR) with allogeneic mo
nonuclear cells (MNCs) and coculture of allogeneic dendritic cells (DCs) wi
th HMCL expressing transgenic CD40L were used to evaluate the APC function
of modified HMCL as well as the role of bystander DCs in inducing an anti-t
umor immune response.
Results. CD40L expression significantly inhibited the growth of the CD40(+)
HMCL and induced apoptosis. These effects were less evident for the CD40-
HMCL. There was no upregulation of costimulatory molecules on either HMCL f
ollowing CD40L expression. Both HMCL expressing transgenic CD40L induced ma
turation of bystander DCs and enhanced their ability to stimulate the proli
feration of MNCs. DCs cultured with the poorly immunogenic RPMI 8226 expres
sing CD40L upregulated T-lymphocyte release of IFN-gamma and other Th1 cyto
kines (interleukin-2, tumor necrosis factor-alpha).
Conclusions. Our data suggest that transgenic expression of CD40L exerts a
dual effect favoring generation of an immune response to human MM. Where th
e tumor cells are CD40(+), the engagement of CD40 antigen by CD40L on tumor
cells induces their apoptosis, allowing uptake of tumor-associated antigen
by professional APC. Independently of tumor-cell expression of CD40, trans
genic expression of CD40L on tumor cells allows them to stimulate CD40(+) A
PC, to increase their maturation and their capacity to stimulate cytotoxic
T lymphocytes (CTL) that recognize the tumor-derived antigens the APC may h
ave engulfed. (C) 2001 International Society for Experimental Hematology. P
ublished by Elsevier Science.