CD4 cell count <200/μL is a sensitive biomarker to identify non-HIV immunocompromised patients who are at risk for PJP. Measuring CD4 cell counts could help clinicians identify patients who may benefit from TMP-SMX prophylaxis.

IntroductionCystic fibrosis (CF) is a severe monogenic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Several types of CFTR modulators (correctors/potentiators) have been developed to overcome protein dysfunction associated with these mutations. CFTR modulator therapy is now available for the major CF-causing mutations, however 10% of people with CF remain without causal treatments. By combining investigational and market approved CFTR modulators, we aimed to maximise functional rescue of iva-, luma- and tezacaftor refractory mutants G85E and N1303K.MethodsWe used the well-established forskolin induced swelling (FIS) in primary rectal organoids to assess responses to different CFTR corrector and potentiator types. The FIS analysis was performed with brightfield microscopy, allowing both 1 h and 24 h follow-up. Corrector and potentiator activity of elexacaftor was investigated.ResultsFor G85E, maximal rescue was observed by a combination of elexacaftor and corr4a. For N1303K, the quadruple combination teza-elexa-ivacaftor with apigenin was required to obtain a rescue similar to that of luma-ivacaftor rescued F508del. Elexacaftor rescued G85E and N1303K by different mechanisms, with chronic corrector effects on G85E and acute potentiation of N1303K only in the presence of ivacaftor. Synergy in N1303K rescue for iva-elexacaftor and apigenin suggests at least three potentiator mechanisms for this mutant. 24 h FIS identified ivacaftor as the main CFTR modulator for N1303K and elexacaftor and apigenin as co-potentiators.ConclusionsNovel combinations of CFTR modulators can further improve functional rescue of G85E and N1303K in rectal organoids, although for N1303K more effective CFTR modulators are still needed.

Diagnosing cystic fibrosis (CF) when sweat chloride is not in the CF range and less than 2 disease-causing CFTR mutations are found requires physiological CFTR assays, which are not always feasible or available. We developed a new physiological CFTR assay based on the morphological differences between rectal organoids from subjects with and without CF. In organoids from 167 subjects with and 22 without CF, two parameters derived from a semi-automated image analysis protocol (rectal organoid morphology analysis, ROMA) fully discriminated CF subjects with two disease-causing mutations from non-CF subjects (p<0.001). ROMA, feasible at all ages, can be centralised to improve standardisation.