Usefulness of interim analyses in portending study results in antipsychotic and antidepressant trials

It is unknown whether interim analyses portend final study results. Fatigue, pressure to complete trials and recruitment differences may mitigate against this. We examined the similarity of efficacy results of the first and second half of recruited patients to complete trials and explore possible intervening variables. Using data from the NewMeds repository of patient level data from placebo-controlled randomized trials of antipsychotics (AP) (22 studies, n=7056) and antidepressants (AD) (39 studies, n=12,217) we compared treatment effect size (placebo vs. active treatment) of the first and second half of patients recruited in completed trials. We found that in AP studies median difference in treatment effect between cohorts was -0.03, indicating that overall first and second cohorts yielded similar results. In AD studies, median difference between cohorts was 0.04, indicating that overall the second cohort had slightly larger active-placebo-difference. Overall, on average there were minimal differences in effect size between the first and the second cohorts, and in 30 of 39 trials interim results were a good estimate of the results on the 2nd cohort. In AD trials first and second cohort results were more similar when the proportion of patients per study centre and recruitment time of the two cohorts was similar. Results suggest that interim analyses in AD and AP studies may reliably serve to estimate ultimate effects and, at least in AD trials, are more accurate when the same sites are used to a similar extent and recruitment time of the two consequent cohorts is similar.

Dynamics of early T cells: prothymocyte migration and proliferation in the adult mouse thymus

The object of this review has been to consider precursor cell migration into the normal adult thymus, using the mouse model. We have presented a series of experiments and discussed them in the context of other relevant experiments in the literature. The conclusions, qualified in the text, can be summarized as follows: There is a continual input of precursor cells into the normal undepleted adult thymus. The daily input of precursors under normal circumstances is very low (e.g. several per day). Once a precursor enters the pool of proliferating cells inside the thymus, its proliferation is limited to only several weeks. There is no permanent endogenous stem cell. There are a number of different precursor microenvironments in the thymus with different controls, since the kinetics of early (bone marrow-derived) and late (thymus-derived) precursors is quite different. All of these points require further analysis, and we have presented a minimal model as a basis for further experiment.