key: cord-0975691-hj2205b0 authors: Murphy, William J. title: The Need for More Basic Research on SARS-Cov2 Infection and Vaccines on Potential Psychoneurological Effects Using Maternal Immune Activation (MIA) Modeling date: 2021-07-01 journal: Brain Behav Immun DOI: 10.1016/j.bbi.2021.06.009 sha: a0a184d0dc300d0b02bb537364a311525169af5e doc_id: 975691 cord_uid: hj2205b0 The rapid development and application of different SARS-Cov2 vaccines world-wide has resulted in impressive efficacy and protection from the pandemic. However, the existence of different and continuously developing vaccine candidates coupled with the likelihood of continued application due to both waning immune responses and emergence of viral mutants, means that more basic research regarding their efficacy and continued application are needed. This is particularly true with use of preclinical models involving effects when given during pregnancy. The substantial body of data on the impact of maternal immune activation (MIA) on neurologic development and behavior in the progeny necessitates the need to have all vaccine candidates, particularly when inducing strong toll receptor (TLR) responses, involving these models. However, to foster these types of basic research studies involving different vaccine products, initiatives must first be implemented by the NIH and FDA even while clinical data still accumulates. Abstract: The rapid development and application of different SARS-Cov2 vaccines world-wide has resulted in impressive efficacy and protection from the pandemic. However, the existence of different and continuously developing vaccine candidates coupled with the likelihood of continued application due to both waning immune responses and emergence of viral mutants, means that more basic research regarding their efficacy and continued application are needed. This is particularly true with use of preclinical models involving effects when given during pregnancy. The substantial body of data on the impact of maternal immune activation (MIA) on neurologic development and behavior in the progeny necessitates the need to have all vaccine candidates, particularly when inducing strong toll receptor (TLR) responses, involving these models. However, to foster these types of basic research studies involving different vaccine products, initiatives must first be implemented by the NIH and FDA even while clinical data still accumulates. The extraordinary nature of the SARS-Cov2 pandemic has resulted in an unprecedented acceleration in the development of multiple vaccine candidates (RNA, DNA and protein-based), and having shown considerable efficacy and an acceptable safety profile, they are now being broadly applicated to adults, including pregnant women. Therein lies a potential concern. The importance of having vaccines available to this at-risk population is unquestionable with SARS-Cov2 given the severity of its pathology and the urgency of the pandemic. The impact of SARS-Cov2 infection on both the mother and fetus could be significant, especially with recent reports of infection resulting in maternal immune activation (MIA) at the placental interface, a phenomenon that has been associated with an increased risk of progeny developing autism 1 . These newer RNA-based and adenoviral-based gene delivery approaches may exert broader effects than the specification of a protein sequence, and coupled with the existence of the multiple vaccine products in use with a push for more to be developed, the amount of preclinical vetting per vaccine candidate has been diluted. Additionally, the emergence of viral variants, as well as evidence of waning immune protection, indicates that it is likely that further administration of these and/or further modified vaccines will be necessary for the foreseeable future. Surprisingly though, robust preclinical assessments pertaining to these issues have been seriously lacking. This is especially true now as there has simply been not time for robust assessment of possible long-term off-target effects or risk factors that may impact them either clinically or preclinically. Simply because clinical application has been initiated should not preclude doing such assessments now, not only to be proactive, but for also optimizing efficacy. Different preclinical models employed have a huge impact on their ability to detect any potential short or long-term effects and what can be safely used in an adult should not be automatically extrapolated to be safe in all stages of life and development. Case in point, a substantial body of literature in multiple preclinical models, from laboratory mice to non-human primates (NHP), demonstrate that the administration of toll-like receptor (TLR) agonists, such as poly I:C, a synthetic double-stranded RNA (dsRNA) analog which primarily signals via TLR3, and TLR4 agonists such as LPS, during pregnancy results in maternal immune activation (MIA), culminating with the manifestation of abnormal behaviors in the progeny resembling autism and schizophrenia 2,3 . These behavioral alterations are associated with marked transcriptomic changes in neuronal gene and immune pathways in the progeny 4 . While there is no evidence on whether these neurological effects can be observed when such stimuli are applied to adults, inherently limiting preclinical models in their ability to directly extrapolate their results to humans, it is fortunate such models exist to even attempt to mirror human neuropsychiatric conditions preclinically. Therefore, the effects of both RNA-based and adenoviral-based vaccines given during pregnancy and potential neuropsychiatric effects on their offspring merits closer inspection through extensive utilization of these models. Different vaccine modalities can have different immunological effects and do indeed differ from the stimuli used in prior MIA modeling. RNA-based vaccines are single-stranded RNA (ssRNA) primarily signal via TLR7/8, delineating them from poly I:C. These signaling paradigms are not as restricted as once thought, however, as even ssRNA has been also demonstrated to trigger via TLR3 5,6 . Furthermore, recent reports suggest that TLR7 agonists can also induce MIA resulting in similar effects on the progeny 7 . While RNA modifications, such as those applied in current vaccine formulations, have been shown to reduce these cytokine-inducing effects as demonstrated by in vitro assays suggesting possible lesser systemic immune reactions 8 , these in vitro immune assessments are severely limited in scope and are inadequate substitutes for complex in vivo immune responses evaluated at different stages in development. The paucity of in vivo studies that have been reported primarily focused on assessment of protective immune responses or evaluation of early overt toxicities by using young lean mice and then extrapolating these results to the pregnant condition. However, RNA editing during neonatal brain development is a tightly regulated process, making these stages particularly vulnerable to perturbations that may not occur until after birth or even have a delayed emergence into adulthood, potentially not being revealed unless assessed by behavioral assays. Furthermore, assuming lesser immune responses are automatically less of a risk may not hold true, as recent data using the poly I:C mouse model suggests that intermediate levels of mouse MIA confer the greatest risk for brain development and behavioral alterations in the progeny, with higher levels appearing protective, indicating the complexity of the phenomena 9 . These models, while imperfect, still can provide critical insights, especially as the data with NHP provides a pivotal link to potential human responses. Other factors outside of the ssRNA or adenoviral DNA delivery itself can also potentially impact immune responses to vaccines. The nano-liposomal formulations used in the RNA vaccine delivery platform appear to elicit inflammatory responses 10 which likely also contribute to the systemic effects observed. Another important parameter revolves around the status of the recipient. Heightened pro-inflammatory responses observed in aged and obese mouse models 12, 13 have been shown to intensify immunopathology and incur a higher risk of mortality, as has been demonstrated with cancer immunotherapy toxicities which would otherwise not be observable in young healthy mice. SARS-Cov2 spike protein, the antigen encoded by the vaccines, has recently been demonstrated to directly trigger TLR2 inflammatory responses by different cell-types, which could be amplified depending on the recipient 11 . As this is the predominant antigen targeted with vaccines, this would suggest that even non-RNA based vaccines may have potential effects depending on the stage of development and should be assessed on this suspicion. Thus, any new type of vaccine application in pregnancy, especially when coupled with obesity or increased age, should probably not be automatically assumed to be without risk to fetal brain development because it is deemed safe in non-obese and/or non-pregnant preclinical models. Given the now broad use of these different vaccines to the general population and increasing pressure for compliance, the NIH and the FDA should immediately prioritize evaluation of these novel vaccines by using these preclinical MIA models in tandem with the incorporation of human modifying variables such as age and obesity. Simply arguing on the merits of differences between current vaccine formulations from prior vaccines or inference from in vitro data does not suffice to assuage potential risks. This is particularly important given the recent and persistent vocal public backlash regarding vaccines overall and the attempts to link them with autism fueled, in large part, by misinformation or misinterpretation of the scientific literature. However, it is critical that this adverse environment not inhibit or adversely impact reasonable scientific discourse on hypothesis-driven research or be viewed as a valid condemnation of vaccines. There is little doubt of the critical need for vaccines to be applied to all aspects of the population, and it is hoped that all SARS-Cov2 vaccines are safe and effective in pregnancy for both the mother and fetus in the same way the vaccine has been shown to be for healthy nonpregnant adults. However, the safety of these newer vaccine products needs to be coincided with continuous preclinical evaluation (including effects of repeated administration) using appropriate models involving multiple parameters. It is fortunate that different vaccine classes are available for use as it may be possible to tailor certain ones towards different at-risk populations. Robust preclinical research is needed though, as waiting for clinical outcome data will likely take many years and still leave a gap in mechanistic dissection, and without concurrent evaluation using accepted models, this could undermine the acceptance of not only these novel vaccine modalities, but future vaccine recommendations as well. While the importance and benefits of vaccination cannot be understated, especially at this critical junction in the SARS-Cov2 pandemic, it is only through continuous rigorous scientific scrutiny that reassurances on safety will be achievable and that these vaccines will be fully optimized. 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