[1] Dana Farber Canc Inst, Div Human Retrovirol, Boston, MA 02115 USA
[2] Harvard Univ, Sch Med, Ctr Blood Res, Boston, MA 02115 USA
[3] Harvard Univ, Sch Med, Dept Pathol, Boston, MA 02115 USA
[4] Harvard Univ, Sch Publ Hlth, Dept Canc Biol, Boston, MA 02115 USA
[5] Childrens Hosp, Ina Sue Perlmutter Lab, Boston, MA 02115 USA
[6] Beth Israel Hosp, Dept Med, Boston, MA 02215 USA
[7] Beth Israel Hosp, Dept Pediat, Boston, MA 02215 USA
[8] Harvard Univ, Sch Med, Boston, MA 02115 USA
[9] Univ Padua, Inst Microbiol, I-35121 Padua, Italy