Rationale Pneumococcal pneumonia remains a global health problem. Pneumococcal colonisation increases local and systemic protective immunity, suggesting nasal administration of live attenuated S. pneumoniae strains could help prevent infections.

Objectives We used a controlled human infection model to investigate whether nasopharyngeal colonisation with attenuated S. pneumoniae strains protected against re-colonisation with wild-type (WT) S. pneumoniae (Spn).

Methods Healthy adults aged 18-50 years were randomised (1:1:1:1) for nasal administration twice (two weeks interval) with saline, WT Spn6B (BHN418) or one of two genetically modified Spn6B strains - SpnA1 (Δfhs/piaA) or SpnA3 (ΔproABC/piaA) (Stage I). After 6 months, participants were challenged with SpnWT to assess protection against re-colonisation (Stage II).

Measurements and Main Results 125 participants completed both study stages as per intention to treat. No Serious Adverse Events were reported. In Stage I, colonisation rates were similar amongst groups: SpnWT 58.1% (18/31), SpnA1 60% (18/30) and SpnA3 59.4% (19/32). Anti-Spn nasal IgG levels post-colonisation were similar in all groups whilst serum IgG responses were higher in the SpnWT and SpnA1 groups than the SpnA3 group. In colonised individuals, increases in IgG responses were identified against 197 Spn protein antigens and serotype 6 capsular polysaccharide using a pangenome array. Participants given SpnWT or SpnA1 but not SpnA3 in phase 1 were partially protected against re-colonisation with SpnWT (recolonisation rates of 29% versus 30% respectively).

Conclusion Nasal colonisation with genetically modified live attenuated Spn was safe and induced protection against recolonisation, suggesting nasal adminstration of live attenuated Spn could be an effective stategy for preventing pneumococcal infections.

The authors have declared no competing interest.

ISRCTN22467293

This study was funded by MRC

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Approvals were given by the Health Research Authority National Research Ethics Service Liverpool East (18/NW/0481) and the Department for Food Rural and Agricultural Affairs (DEFRA) for the deliberate release of a GMO under schedule 2 of the Genetically Modified (Deliberate Release) Regulations 2002 Ref 18/R51/01

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

↵# joint senior authors

ISRCTN registry: ISRCTN22467293

Funding: Funded by Bill and Melinda Gates Foundation (OPP1117728) and the Medical Research Council awards (MR/M011569/1 and MR/N016874/1). JSB, RH, CMW and ERS work at UCLH/UCL which received funding from the Department of Health’s NIHR Biomedical Research Centre’s funding scheme. RSH is a NIHR Senior Investigator.

All data produced in the present study are available upon reasonable request to the authors