Event rates and incidence of post-COVID-19 condition in hospitalised SARS-CoV-2 positive children and young people and controls across different pandemic waves: exposure-stratified prospective cohort study in Moscow (StopCOVID).

BACKGROUND: Long-term health outcomes in children and young people (CYP) after COVID-19 infection are not well understood and studies with control groups exposed to other infections are lacking. This study aimed to investigate the incidence of post-COVID-19 condition (PCC) and incomplete recovery in CYP after hospital discharge and compare outcomes between different SARS-CoV-2 variants and non-SARS-CoV-2 infections. METHODS: A prospective exposure-stratified cohort study of individuals under 18 years old in Moscow, Russia. Exposed cohorts were paediatric patients admitted with laboratory-confirmed COVID-19 infection between April 2 and December 11, 2020 (Wuhan variant cohort) and between January 12 and February 19, 2022 (Omicron variant cohort). CYP admitted with respiratory and intestinal infections, but negative lateral flow rapid diagnostic test and PCR-test results for SARS-CoV-2, between January 12 and February 19, 2022, served as unexposed reference cohort. Comparison between the 'exposed cohorts' and 'reference cohort' was conducted using 1:1 matching by age and sex. Follow-up data were collected via telephone interviews with parents, utilising the long COVID paediatric protocol and survey developed by the International Severe Acute Respiratory and Emerging Infection Consortium (ISARIC). The WHO case definition was used to categorise PCC. RESULTS: Of 2595 CYP with confirmed COVID-19, 1707 (65.7%) participated in follow-up interviews, with 1183/1707 (69%) included in the final 'matched' analysis. The median follow-up time post-discharge was 6.7 months. The incidence of PCC was significantly higher in the Wuhan variant cohort (89.7 cases per 1000 person-months, 95% CI 64.3-120.3) compared to post-infection sequalae in the reference cohort (12.2 cases per 1000 person-months, 95% CI 4.9-21.9), whereas the difference with the Omicron variant cohort and reference cohort was not significant. The Wuhan cohort had higher incidence rates of dermatological, fatigue, gastrointestinal, sensory, and sleep manifestations, as well as behavioural and emotional problems than the reference cohort. The only significant difference between Omicron variant cohort and reference cohort was decreased school attendance. When comparing the Wuhan and Omicron variant cohorts, higher incidence of PCC and event rates of fatigue, decreased physical activity, and deterioration of relationships was observed. The rate of incomplete recovery was also significantly higher in the Wuhan variant cohort than in both the reference and the Omicron variant cohorts. CONCLUSIONS: Wuhan variant exhibited a propensity for inducing a broad spectrum of physical symptoms and emotional behavioural changes, suggesting a pronounced impact on long-term health outcomes. Conversely, the Omicron variant resulted in fewer post-infection effects no different from common seasonal viral illnesses. This may mean that the Omicron variant and subsequent variants might not lead to the same level of long-term health consequences as earlier variants.

Severe defect in thymic development in an insertional mutant mouse model.

Transgenic mice were generated expressing NK1.1, an NK cell-associated receptor, under control of the human CD2 promoter. Unexpectedly, one of the founder lines, Tg66, showed a marked defect in thymic development characterized by disorganized architecture and small size. Mapping of the transgene insertion by fluorescence in situ hybridization revealed integration in chromosome 2, band G. Already from postnatal day 3, the thymic architecture was disturbed with a preferential loss of cortical thymic epithelial cells, a feature that became more pronounced over time. Compared with wild-type mice, total thymic cell numbers decreased dramatically between 10 and 20 days of age. Thymocytes isolated from adult Tg66 mice were predominantly immature double-negative cells, indicating a block in thymic development at an early stage of differentiation. Consequently, Tg66 mice had reduced numbers of peripheral CD4(+) and CD8(+) T cells. Bone marrow from Tg66 mice readily reconstituted thymi of irradiated wild-type as well as RAG-deficient mice. This indicates that the primary defect in Tg66 mice resided in nonhemopoietic stromal cells of the thymus. The phenotype is observed in mice heterozygous for the insertion and does not resemble any known mutations affecting thymic development. Preliminary studies in mice homozygous for transgene insertion reveal a more accelerated and pronounced phenotype suggesting a semidominant effect. The Tg66 mice may serve as a useful model to identify genes regulating thymic epithelial cell differentiation, thymic development, and function.

Mandatory chromosomal segment balance in aneuploid tumor cells.

BACKGROUND: Euploid chromosome balance is vitally important for normal development, but is profoundly changed in many tumors. Is each tumor dependent on its own structurally and numerically changed chromosome complement that has evolved during its development and progression? We have previously shown that normal chromosome 3 transfer into the KH39 renal cell carcinoma line and into the Hone1 nasopharyngeal carcinoma line inhibited their tumorigenicity. The aim of the present study was to distinguish between a qualitative and a quantitative model of this suppression. According to the former, a damaged or deleted tumor suppressor gene would be restored by the transfer of a normal chromosome. If so, suppression would be released only when the corresponding sequences of the exogenous normal chromosome are lost or inactivated. According to the alternative quantitative model, the tumor cell would not tolerate an increased dosage of the relevant gene or segment. If so, either a normal cell derived, or, a tumor derived endogenous segment could be lost. METHODS: Fluorescence in Situ Hybridization based methods, as well as analysis of polymorphic microsatellite markers were used to follow chromosome 3 constitution changes in monochromosomal hybrids. RESULTS: In both tumor lines with introduced supernumerary chromosomes 3, the copy number of 3p21 or the entire 3p tended to fall back to the original level during both in vitro and in vivo growth. An exogenous, normal cell derived, or an endogenous, tumor derived, chromosome segment was lost with similar probability. Identification of the lost versus retained segments showed that the intolerance for increased copy number was particularly strong for 3p14-p21, and weaker for other 3p regions. Gains in copy number were, on the other hand, well tolerated in the long arm and particularly the 3q26-q27 region. CONCLUSION: The inability of the cell to tolerate an experimentally imposed gain in 3p14-p21 in contrast to the well tolerated gain in 3q26-q27 is consistent with the fact that the former is often deleted in human tumors, whereas the latter is frequently amplified. The findings emphasize the importance of even minor changes in copy number in seemingly unbalanced aneuploid tumors.

Microcell-mediated chromosome transfer provides evidence that polysomy promotes structural instability in tumor cell chromosomes through asynchronous replication and breakage within late-replicating regions.

It was reported earlier that normal chromosome 3 (chr3) transfer into tumor cells of different origin may suppress their ability to grow in SCID mice. Tumorigenicity may be restored by the loss of certain 3p regions. We transferred a normal cell-derived chr3 into cells of a human renal cell carcinoma line and followed the chromosomal changes during in vivo and in vitro growth. In cells cultivated for 6 weeks or more and in the tumors grown in SCID mice, supernumerary chrs3 were always rearranged, accompanied by 3p losses. Unexpectedly, we found that the rearrangements affected not only the transferred exogenous chr3, but also the endogenous chrs3. Other chromosomes that were polysomic in the recipient cells were affected as well, suggesting that polysomy may be associated with structural chromosome instability. The dominant chromosomal aberrations were unbalanced translocations with preferentially pericentromeric breakpoints. The breakpoint distribution on chr3 preferentially affected the pericentromeric 3p11 (8 breaks) and 3p12-13 (5 breaks) regions. The regions 3p14 and 3q26-27 occasionally were involved as well (one break in each case). These four regions were the latest replicating, as shown by BrdU incorporation-based replication banding. Using fluorescence in situ hybridization-based replication timing, we detected asynchronous and incomplete centromere replication in cells with 3 or 4 copies of chr3, but not in cells with 2. We concluded that in tumor cells, asynchronous and incomplete replication of polysomic chromosomal parts is associated with aberrations that have breakpoints within the late-replicating regions. This may explain the increased structural chromosome instability and preferential pericentromeric localization of breakpoints in hyperploid tumors.

Coincidence of synteny breakpoints with malignancy-related deletions on human chromosome 3.

We have found previously that during tumor growth intact human chromosome 3 transferred into tumor cells regularly looses certain 3p regions, among them the approximately 1.4-Mb common eliminated region 1 (CER1) at 3p21.3. Fluorescence in situ hybridization analysis of 12 mouse orthologous loci revealed that CER1 splits into two segments in mouse and therefore contains a murine/human conservation breakpoint region (CBR). Several breaks occurred in tumors within the region surrounding the CBR, and this sequence has features that characterize unstable chromosomal regions: deletions in yeast artificial chromosome clones, late replication, gene and segment duplications, and pseudogene insertions. Sequence analysis of the entire 3p12-22 revealed that other cancer-associated deletions (regions eliminated from monochromosomal hybrids carrying an intact chromosome 3 during tumor growth and homozygous deletions found in human tumors) colocalized nonrandomly with murine/human CBRs and were characterized by an increased number of local gene duplications and murine/human conservation mismatches (single genes that do not match into the conserved chromosomal segment). The CBR within CER1 contains a simple tandem TATAGA repeat capable of forming a 40-bp-long secondary hairpin-like structure. This repeat is nonrandomly localized within the other tumor-associated deletions and in the vicinity of 3p12-22 CBRs.

The microcell hybrid-based "elimination test" identifies a 1-Mb putative tumor-suppressor region at 3p22.2-p22.1 centromeric to the homozygous deletion region detected in lung cancer.

We have previously shown that inoculation of human chromosome 3 (chr3)/A9 mouse fibrosarcoma microcell hybrids (MCHs) into severely combined immunodeficient (SCID) mice was followed by the regular elimination of certain 3p regions, whereas a 3q region was retained even after prolonged mouse passage. Using this approach, referred to as the elimination test (Et), we identified a common eliminated region (CER) of about 7 cM at 3p22-p21.3 that was absent in all tumors generated from five MCHs. A second frequently eliminated region (FER, originally called ER2) was found at 3p21.1-p14.2. These segments have been reported to be frequently deleted in a variety of carcinomas. In the following experiments, we have identified at the centromeric border of CER a common eliminated region 1 (CER1) of about 1.6 cM. We now report the results of more detailed analyses of the original tumor panel that contained 30 SCID mouse tumors. Using polymerase chain reaction and chromosome reverse painting, we have identified at the telomeric border of CER a second common eliminated region (designated as CER2). CER2 is flanked distally by RH94338 and proximally by SHGC-154057. The size of CER2 is about 1 Mb, according to the Homo Sapiens Complete Genome databases at EMBL, and is located about 0.5 Mb centromeric to the known homozygous deletion region, identified in lung cancer. Remarkably, two chemokine-receptor genes (CCRs), CCR8 and CX3CR1, are located within CER2, whereas seven CCRs were found within CER1.