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After a transplant or intensive chemotherapy, the part of the immune system that makes new kinds of T cell recovers slowly in adults and sometimes not at all. The deficit is well described, well measured and currently not correctable.
The transplant facet of this round put the gap in a sentence: there is no randomised evidence that any intervention accelerates thymic recovery in adults, and the agents trialled for it, including thymic peptides, keratinocyte growth factor, growth hormone and sex steroid blockade, have not produced a treatment in routine use.
The consequence is specific rather than general. Cell counts come back; the repertoire does not. Normal numbers of T cells can coexist with a narrowed range of things those T cells can recognise, which is why a normal count can reassure falsely, and why repertoire measurement remains a research tool rather than a clinical test. For a person this shows up as susceptibility to infections years after counts normalised, as vaccine responses that are weaker than the schedule assumes, and as the reason revaccination exists as a programme at all.
It is a moderate rather than a critical bottleneck because the problem is largely managed around rather than solved: prophylaxis by phase, immunoglobulin replacement where antibodies are low, and revaccination schedules do most of the work, and the honest framing is that these substitute for an immune system rather than rebuild one. The commonest failure in practice is not biological at all, it is that nobody owns the revaccination schedule between the transplant centre and primary care.
What would change it is a trial, and the reason there has not been one is partly that the readout is contested. Thymic output can be estimated from T-cell receptor excision circles, repertoire diversity can be sequenced, and neither has been accepted as an endpoint that a regulator would license a drug against. An intervention that moved a repertoire measure without changing infection rates would not be worth having, and an intervention that reduced infections would be adopted whatever it did to the thymus, which is the design problem.
Shares Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.
Shares Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.
Shares Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.
Shares Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.
Shares Revaccination after transplant: the schedules, and where the UK and the US differ, Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.
Shares B-cell aplasia and low antibodies after CAR-T and bispecifics, and immunoglobulin replacement, Rebuilding an immune system: the timeline, lineage by lineage, Infection risk after transplant and cell therapy, phase by phase, and the prophylaxis that follows it and the tags rejuvenation, survivorship.
Shares Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.
Shares Recovery and rejuvenation roadmap: cure is not enough → survivorship gets a name → the cohorts that measured the cost → exercise proven as treatment → biological ageing measured and sold → repair, if anyone funds it and the tags rejuvenation, survivorship, open-problem.