Pk. Wallace et al., Exogenous antigen targeted to Fc gamma RI on myeloid cells is presented inassociation with MHC class I, J IMMUNOL M, 248(1-2), 2001, pp. 183-194
Vaccine therapy is attractive for prostate cancer patients because the tumo
r is slow growing (allowing time to augment host responses) and occurs in a
n older population less likely to tolerate more toxic treatments. We have c
onstructed an expression vector based on a monoclonal antibody (mAb) that t
argets the high affinity receptor for IgG (Fc gamma RI, CD64) which is excl
usively expressed on myeloid cells including dendritic cells (DC). The heav
y chain of mAb H22 CH2 and CH3 domains were removed and replaced with the g
ene for prostate specific antigen (PSA). Using that vector, we have constru
cted and purified FPH22.PSA, a fusion protein that targets PSA to Fc gamma
RI on antigen presenting cells (APC). This fusion protein has an apparent m
olecular mass of 80-83 kDa, binds to Fc gamma RI with high affinity and exp
resses PSA. We demonstrate that FPH22.PSA targeted PSA was internalized and
processed by the human myeloid THP-I cell line resulting in presentation o
f MHC class I-associated PSA peptides and lysis of THP-1 by PSA-specific hu
man CTL. Moreover, pretreatment of THP-I cells with antibodies to block eit
her Fc gamma RI or MHC class I, blocked lysis indicating that targeting to
Fc gamma RI results in presentation of exogenous antigen on MHC class I mol
ecules. These data demonstrate that FPH22.PSA was processed in such a manne
r by the myeloid cell line to allow for presentation of immunodominant pept
ides in MHC class I molecules and suggests that uptake of antigen via Fc ga
mma RI results in cross-priming. (C) 2001 Elsevier Science BN. All rights r
eserved.