Figure 6.

Blood TRM-like cells can be used to estimate the hazard of malaria diagnosis after CHMI. (A) Sampling workflow. Thirty-one volunteers across all vaccination groups were sampled at several time points following IV viral vector (IV+ timepoints) and around controlled human malaria infection. One volunteer from this cohort was not challenged. Five more control (non-vaccinated) volunteers were challenged and followed up at pre- and post-challenge time points, only. All volunteers were treated with standard anti-malarial therapy at day 21 post-CHMI or, if earlier, when they met our diagnostic criteria for malaria (see methods). (B) TRM-like cells after IV administration of viral vector. Frequency of circulating CD69+CD11ahi cells (as a proportion of CD8+CD45RA- cells) by time point. Comparisons were assessed using ratio paired t tests. Lines represent significant differences between the bound groups; bars show mean and standard deviation. (C) The GMFI of TRM-like cell CXCR6 at three different time points following IV viral vector. Comparisons were assessed using ratio paired t tests. Lines represent significant differences between the bound groups; bars show mean and standard deviation. Matched GMFI values of CD69- cells are also presented for reference. *** represents a p value < 0.0001. (D) Kaplan Meier curve using TRM-like cells 3 days after IV viral vector to stratify volunteers. Volunteers were stratified according to whether their TRM-like cell fraction (as a proportion of CD8+ CD45RA- cells) at day 3 after IV viral vector was above or below the median of all values. A log-rank test was performed to test for difference in survival (delay/lack of malaria diagnosis). The risk table shows the percentage of volunteers, in each stratum, at risk of malaria diagnosis at five representative time points. Right censoring occurred at 21 days as all undiagnosed volunteers received antimalarial therapy at this time. (E) Univariate Cox regression models using TRM−like cells [CD69+ CD11a hi frequency (% CD45RA- CD8+ CD3+ T cells)] measured at two time points. Each regression model estimated the effect that the variable had on an individual’s hazard of being diagnosed with malaria after CHMI. Hazard ratios less than one suggested that an increase in the TRM−like cell frequency decreased the instantaneous risk of malaria diagnosis over the study period. Hazard ratios greater than one suggested that a decrease in TRM−like cell frequency increased the instantaneous risk of malaria diagnosis over the study period. Log transformation was applied to the TRM−like cell frequency, and regression was performed on these values. The p value was calculated using a Wald test, with a null hypothesis that the parameter did not alter the hazard of malaria diagnosis after CHMI. (F) Multivariate Cox regression model using TRM like cells [CD69+ CD11a hi frequency (% CD45RA- CD8+ CD3+ T cells)] measured at two time points: IV and IV+3. Hazard ratios and 95%CI are presented. Log transformation was applied to the TRM−like cell frequency, and regression was performed on these values. The individual variable p values were calculated using a Wald test. The global p value was calculated using a Score (log−rank) test. Events refers to the number of volunteers that were diagnosed with malaria. AIC, Akaike information criterion; C, challenge; CHMI, controlled human malaria infection; D, day; GMFI, geometric mean fluorescence intensity; IV, intravenous viral vector administration; TRM, tissue-resident memory T cell.