A blessing and a curse: is high NK cell activity good for health and bad for reproduction?

A Blinded Investigation: Accentuated NK Lymphocyte CD335 (NKp46) Expression Predicts Pregnancy Failures

AIM

NKp46 is an NK cell receptor uniquely expressed by NK cells and a small subset of innate lymphoid cells. In our previous studies, we suggested a tight connection between the activity of NK cells and the expression of NKp46 and supported the clinical significance of NKp46 expression in NK cells in women with reproductive failures. In this study, we investigated the expression of NKp46 in NK cells in the peripheral blood of women in early pregnancy and analyzed its association with pregnancy loss.

METHODS

In a blinded study, we examined blood samples and analyzed the subsequent pregnancy outcomes from 98 early pregnant women (5th-7th week of gestation-w.g.) and 66 women in the 11th-13th week of pregnancy who served as controls. We studied the expression of NKp46 and the levels of anti-cardiolipin antibodies (aCL). The results of aCL were shared with the clinic, while the expression of NKp46 was blinded and not analyzed until the end of the study.

RESULTS

A misbalance in the NKp46⁺NK cells subpopulations was associated with an unfavorable ongoing pregnancy. A decreased level of NKp46^high cells (<14%) was strongly associated with miscarriage. A decreased level of the double-bright subpopulation (NKp46^hightCD56⁺⁺) also was a negative prognostic factor for the pregnancy course, but its increased level (>4%) was strongly associated with a successful pregnancy course.

CONCLUSIONS

Our results showed that accentuated levels of NKp46⁺NK cells lead to a negative prognosis for early pregnancy courses in women.

A blinded multicenter investigation: Accentuated NK lymphocyte CD335 (NKp46) expression predicts reproductive failures after IVF

The peripheral blood NK cell diversity is highly complex. Recent studies have described more than a thousand phenotypes sharing NK cell receptors (NKRs), across the leukocyte lineages. Previously, we have found that accentuated NK p46 phenotype has prognostic value for NK cytotoxicity status, and is characteristic for patients with recurrent implantation failure (RIF). In a blinded investigation we studied blood samples from IVF women before embryo transfer (pre-implantation genetic tested [PGT] embryos n = 116; not tested embryos n = 219). We studied NKp46 expression by flow cytometry and anti-cardiolipin antibody (aCL) levels. aCL results were transmitted to the clinic but NKp46 expression was blinded (for us and for the clinic) and not analyzed before termination of the study (end of last pregnancy). Association of NKp46 phenotype with clinical pregnancy rate (CPR), pregnancy failure (PF) rate and life birth rate (LBR) were analyzed. aCL positive and IvIg treated cases were excluded. IVF success was dependent on p46 NK phenotype in patients with PGT embryos. Elevated p46 expression on NK (>93%) as well as decreased (<66%) significantly reduce CPR (OR 12.7 and 3.8) without affecting pregnancy failure frequency. Both accentuations (taken together) resulted in a significant reduction of LBR (OR 3.9 p = 0.019) compared with non-accentuated phenotypes (p46 levels 66-93%). Elevated NK cell levels (>14.5% weakly) were associated with PF (OR 3.1 p = 0.069), but not significantly with reduced LBR. In contrast, numbers of NKCD335+ lymphocytes (>11.5%) were a significant predictor of PF (OR-4.0 p<0.05) and decreased LBR (OR 2.1 p = 0.06). At the same time, accentuated numbers of NKCD335neg lymphocytes (<0.7 and >4%) were also associated with decreased LBR (OR 2,65 p = 0.05). In patients with NKCD335++ numbers (<5 and >21%), we found a weakly association with IVF failure. We found similar associations in IVF patients without PGT -A but at lower significance levels regardless the higher number of patients. Impact of NKp46 phenotype for IVF success was significant in patients with donor's ET and almost imperceptible in patients > 35y.o. with own embryo transfer. Accentuated increased or decreased CD335 expression on NK was associated with embryo implantation failure. Balanced CD335 levels form a condition favorable for implantation. Elevated numbers of p46+NK (CD3-CD56+CD335+) predicts pregnancy failures at higher significance levels than elevated NK cell numbers. Elevated numbers of p46negNK (CD3-CD56+CD335-) indicate reduced LBR. Accentuation of p46 expression on NK cells is associated with reproductive failures. In combination with PGD it provides a powerful prediction algorithm and treatment option.

Prednisolone and enoxaparin (clexane) therapy ('the Bondi protocol') for repeated IVF failure

PROBLEM

What is the impact of an empirical immune therapy protocol of prednisolone and enoxaparin (clexane) (the 'Bondi protocol') on women with repeated in vitro fertilization (IVF) failure?

METHOD OF STUDY

This was a retrospective review of live birth outcomes conducted on all transfer cycles performed by a single clinician (GS) at IVFAustralia between February 2016 and April 2020. This study consisted of 1786 transfer cycles, including 460 cycles treated with the Bondi protocol and 1326 without. Women with repeated IVF failure were given the Bondi protocol based on blood NK cell activity. Primary outcome was live birth and statistical analysis was performed with GraphPad Prism software with significance for P-values < .05.

RESULTS

Overall 'Bondi' and 'normal' protocol cycles had similar rates of IVF/ICSI, fresh/frozen transfers and use of preimplantation genetic testing (PGT). Women given the Bondi protocol were older, had more previous cycles and had higher blood NK cell activity. There was no significant difference in live birth rates (Bondi 26%, normal 28%). Bondi protocol live birth rates per transfer cycle were as high as 40% in patients under 38 years old. The Bondi protocol was more effective as NK activity increased from 'normal' to 'borderline' to 'high'. For high NK cell activity levels, live birth rates were over four times higher for women on the Bondi protocol (28%) than those on normal protocols (6%, P = .0007).

CONCLUSION

This study describes a simple and relatively safe immune therapy protocol that may improve IVF success rates in women with evidence of immune dysfunction.

Expression of natural cytotoxicity receptor NKp46 on peripheral blood natural killer cells in women with a history of recurrent implantation failures

AIM

The peripheral blood natural killer (NK) cells diversity is highly complex; recent studies described more than a thousand phenotypes sharing NK cell receptors, across the leukocyte lineages. In this study, we investigated the expression of NKp46 in peripheral blood NK cells in women with a history of recurrent implantation failures (RIF) with euploid embryos with pre-implantation genetic diagnosis (PGD) and control group (donors of oocytes and surrogate mothers).

METHODS

The expression of NKp46 in peripheral blood lymphocytes and NK cells from women with RIF (n = 57) and control group (n = 50) was analyzed with three-color flow cytometry.

RESULTS

The percentage of NKp46⁺ NK cells was significantly higher in women with RIF compare with the control group and high amount of NKp46⁺ NK cells (>13% of total lymphocytes) was a poor prognostic factor for embryo implantation. Also, women with RIF had a low amount of NKp46^neg NK cells, which was a negative prognostic factor for embryo implantation. The analysis of NK subpopulations, on the basis of NKp46 expression, also revealed that NKp46^neg NK in low amounts (<20% of NK cells) and NKp46^dim in high amounts (>50% of NK cells) are also negative prognostic factors for embryo implantation.

CONCLUSION

Our results support the clinical significance of the NKp46 expression on NK cells in women with RIF. We suggest that the low level of NKp46^neg subset in women with RIF may be a result of an imbalance in the differential development of ILC subsets toward cytotoxic ILC (NK cells), which in turn is a negative condition for successful embryo implantation.

The Genetic Mechanisms Driving Diversification of the KIR Gene Cluster in Primates

The activity and function of natural killer (NK) cells are modulated through the interactions of multiple receptor families, of which some recognize MHC class I molecules. The high level of MHC class I polymorphism requires their ligands either to interact with conserved epitopes, as is utilized by the NKG2A receptor family, or to co-evolve with the MHC class I allelic variation, which task is taken up by the killer cell immunoglobulin-like receptor (KIR) family. Multiple molecular mechanisms are responsible for the diversification of the KIR gene system, and include abundant chromosomal recombination, high mutation rates, alternative splicing, and variegated expression. The combination of these genetic mechanisms generates a compound array of diversity as is reflected by the contraction and expansion of KIR haplotypes, frequent birth of fusion genes, allelic polymorphism, structurally distinct isoforms, and variegated expression, which is in contrast to the mainly allelic nature of MHC class I polymorphism in humans. A comparison of the thoroughly studied human and macaque KIR gene repertoires demonstrates a similar evolutionarily conserved toolbox, through which selective forces drove and maintained the diversified nature of the KIR gene cluster. This hypothesis is further supported by the comparative genetics of KIR haplotypes and genes in other primate species. The complex nature of the KIR gene system has an impact upon the education, activity, and function of NK cells in coherence with an individual’s MHC class I repertoire and pathogenic encounters. Although selection operates on an individual, the continuous diversification of the KIR gene system in primates might protect populations against evolving pathogens.

NK and trophoblast cells interaction: cytotoxic activity on recurrent pregnancy loss

The trial objective was to determine the peripheral blood NK cells cytotoxic activity effect on trophoblast cells at recurrent pregnancy loss (RPL). The investigation involved non-pregnant women with PRL in proliferating and secretory menstrual cycle phases (PMCPh and SMCPh, respectively); women of 6-7 weeks pregnancy with RPL in past medical history; healthy fertile non-pregnant women in PMCPh and SMCPh, women of 6-7 weeks physiological pregnancy, nulliparity healthy women with regular menstrual function in PMCPh and SMCPh. NK cells cytotoxic activity was determined using peripheral blood mononuclear cells. The target cells were JEG-3 line trophoblasts. It has been established that NK cells cytotoxic activity effect on trophoblasts is lower in SMCPh than in PMCPh in non-pregnant fertile women. The NK cells cytotoxic activity was higher in SMCPh than in PMCPh in non-pregnant women with PRL and also higher than the same value in SMCPh in non-pregnant fertile women. The increased NK cells cytotoxic activity values in SMCPh in women with RPL may be the reason for miscarriage.

Revisiting the Functional Impact of NK Cells

Immune responses are critical for the maintenance of homeostasis but can also upset the equilibrium, depending on the context and magnitude of the response. Natural killer (NK) cells are well known for their important roles in antiviral and antitumor immune responses, and they are currently used, mostly under optimized forms, as immunotherapeutic agents against cancer. Nevertheless, with accumulating examples of deleterious effects of NK cells, it is paramount to consider their negative contributions. Here, we critically review and comment on the literature surrounding undesirable aspects of NK cell activity, focusing on situations where they play a harmful rather than a protective role.