Table 1.

SYSTEM	SOURCE	ANTIGEN DEPENDENT OR INDEPENDENT	AMENABLE TO TRANSDUCTION	ANTIGEN PROCESSING	CLINICAL TRIALS	COMMENTS
Cellular
K562	Human erythroleukemia	Both	Yes	Yes	No	Transduced Fc receptors can bind αCD3 or HLA-Ig to allow antigen-specific or non-specific CD8+ T cell expansion Better CD8+ T cell proliferation when expressing 4-1BBL than αCD28 Has been prepared as GMP-compliant stock Might require HLA transduction for antigen presentation
3T3	Murine fibroblast	Both	Yes	Yes	No	Minimal evidence of xenoreactivity Requires HLA transduction for antigen presentation
Insect	Drosophila Schneider S2 cell line	Both	Yes	No	Yes	Lysed at 37°C Exogenous antigen only Minimal evidence of xenoreactivity
Acellular
αCD3/αCD28 beads	Synthetic	Independent	No	No	Yes	Standardized manufacture Excellent control of delivered signals Better CD8+ T cell proliferation when 4-1BBL is substituted for αCD28 Can substitute or add costimulatory or inhibitory molecules
HLA-Ig beads	Synthetic	Dependent	No	No	No	Excellent control of delivered signals Can substitute other HLA-Ig Exogenous antigen loading only