Table II.

Tumor cells engineered to secrete GM-CSF suppress anamnestic CTL response

Tumor	Tumor Size (mm)^b	GM-CSF in vitro (pg/ml)^a	GM-CSF in Vivo (pg/ml)^b	CD11b⁺ Splenocytes^b	Anti-β-Gal Response (LU₃₀/10⁶ Cells)^c
No tumor	Negative	—	ND	1.8	213
B16 wt	17 × 16	0	0	3.0	196
GM42	17 × 16	671	84.5	12.2	<10
GM32	13 × 13	719	301.2	12.0	15
GM15	17 × 14	894	800.7	17.4	<10
GM19	11 × 10	868	115.2	9.3	<10
GM37	17 × 13	690	158.5	13.1	<10
GM34	10 × 10	877	146.0	7.5	14
GM12	18 × 12	702	11.7	8.3	10
GM47	18 × 15	626	172.1	11.2	10

Levels of GM-CSF released by 10⁶ tumor cells after 18 h were evaluated on aliquots of the same cellular preparation injected s.c. to establish the tumor nodules.

Major tumor diameters were measured in a blind fashion immediately before the mice were sacrificed to remove the spleens and set up the peptide-stimulated cultures. On the same day, blood samples were drawn from each mouse to determine the serum levels of GM-CSF (GM-CSF in vivo), and the spleens were analyzed for the presence of CD11b⁺ splenocytes.

LU₃₀ defined as the number of lymphocytes necessary to achieve 30% lysis of 2 × 10³ β-gal peptide-pulsed target cells in a 4-h assay, were calculated from recovered viable cells.