Table 1.

Results of potency and sporozoite membrane integrity assays on the lot of PfSPZ Challenge used in this clinical trial

Time point	Potency (no. of parasites expressing PfMSP-1/well)	% Viability (sporozoite membrane integrity assay)
Fresh	27 ± 4.6	ND
Release	20 ± 1.7	83.3% ± 6.5%
6 Month	18 ± 2.1	86.6% ± 1.9%
9 Month	20 ± 2.1	83.7% ± 8.4%
12 Month	21 ± 1.5	84.8% ± 3.0%
18 Month	20 ± 0.6	83.7% ± 4.2%
24 Month	18 ± 1.0	86.0% ± 1.5%
Pre-1st clinical dose (26 Month)	17 ± 0.6	79.4% ± 6.5%
Post-last clinical dose (30 Month)	16 ± 2.6	87.4% ± 1.9%

Fresh PfSPZ used for the lot of PfSPZ Challenge used in this clinical trial produced 26% more PfMSP-1-expressing parasites in this assay than did PfSPZ that had been cryopreserved for several days (Release); at 30 months, several weeks after inoculation of the last volunteers the PfSPZ had a 40.7% reduction in potency by this assay as compared with fresh PfSPZ. There was no reduction in the results of the sporozoite membrane integrity of cryopreserved PfSPZ during 30 months of storage.

The sporozoite membrane integrity assay was not done on fresh PfSPZ for this particular lot. In our most recent three production campaigns for PfSPZ Challenge, fresh viability was 97.8%, 99.0%, and 98.2%, whereas after cryopreservation viability was reduced to 90.9%, 91.5%, and 87.4%, respectively, a mean reduction of 8.5%.

ND = not done.