Patient cohort
We enrolled 6 patients with GSD1b and 3 controls for this study. Gender, age, inflammatory condition, current medications, absolute neutrophil count (ANC), and c-reactive protein (CRP) levels are provided in Table 1. A deleterious mutation in SLC37A4 gene was identified in all GSD1b patients (Table 1), and all had an ANC below 1000 cells/ mm3, indicative of neutropenia. The average age for the control group was 16.3 years compared to 8.2 years for the GSD1b patients (p = 0.039). Two GSD1b patients also had concurrent IBD, and two patients had signs of bronchiectasis.
Table 1
Subject Demographic and Clinical Data
Sample | M/F | Age | Condition | Drugs | Neupogen | CRP | ANC | Mutation |
GSD1b 1 | M | 3.5 | - | - | yes | 1.34 | 460 | NM_001164277.1 (SLC37A4): c.1042_1043delCT(p.Leu348Valfs*5) |
GSD1b 2 | M | 11.5 | Bronchiectasis | - | yes | 0.55 | 780 |
GSD1b 3 | M | 13.8 | Bronchiectasis | - | yes | 2.1 | 430 |
GSD1b 4 | M | 7 | IBD | Pentasa | yes | 0.3 | 470 | (SLC37A4):c.1211delCT |
GSD1b 5 | M | 12.5 | IBD | Predni- sone | yes | NA | 900 | (SLC37A4):c.1179G > A (p.Trp393*) |
GSD1b 6 | M | 0.7 | - | - | - | 1.9 | 950 | (SLC37A4):c.1041delCT |
control 1 | F | 14.5 | control | - | - | NA | NA | control |
control 2 | F | 17.5 | control | - | - | NA | NA | control |
control 3 | M | 17 | control | - | - | NA | NA | control |
Relevant clinical Information for GSD1b patients and controls. Age in years, CRP in mg/dl, ANC in cells per mm3. CRP and ANC determined at time of draw. Mutation annotation based on genetic testing performed at Sheba Medical Center. |
Reduction in total NK cells and macrophage/monocyte populations characterizes GSD1b
To characterize the immune landscape of the peripheral blood of patients with GSD1b vs. controls, we subjected all leukocytes (CD45+ cells) to unsupervised Rphenograph clustering. Automated clustering of the CD45+ populations identified 33 unique populations. The clusters were manually annotated based on average expression values of each marker in each cluster of combined patient samples displayed in the expression heatmap generated by cytofkit2 (Fig. 1A). Utilizing this method, we were able to identify multiple clusters of naïve T cells including: CD4+ T helper (Th) cells, CD25hiCD127lo regulatory T cells (Treg), CD4−CD8− double neg (DN) T cells, CD8+ cytotoxic T cells (Tc), a population of activated and non-activated T cells and memory T cells. The B cell compartment was represented by naïve B cells, pro-B cell, activated B cells, plasma cells (PC) and anergic B cells. The innate compartment accessible with our methodology consisted of classical pro- and anti-inflammatory macrophages (MΦ), CD16high and CD16low monocytes, monocyte precursors, CD15high and CD15low neutrophils, CD16high and CD16low NK cells, a small granulocyte population (Basophil, Neutrophil, Neutrophil – myeloid derived suppressor cells (MDSC)), and innate lymphoid cells (ILC) (Fig. 1A-C). Cluster 32 could not be assigned to a known immune population because of its atypical high expression of CD11c, CD3 and CD19 and likely represented an immune aggregate or an artifact of unsupervised clustering. Given the low overall abundance of this cluster (0.095% in GSD1b cases and 0.13% in controls), it was labeled as unidentified and excluded from further analysis.
To get an overview of the obtained data and determine the differences in the composition of major immune subtypes, the identified clusters were then arranged into superclusters based on their marker similarities (Fig. 1B-C). There was a significant reduction in NK cells (combined clusters 7 and 25; fold change GSD1b/control 0.395, p value = 0.0375) and myeloid cells (MΦ & monocyte cells, combined clusters 6, 17, 20, 24, 26, and 30; fold change GSD1b/control 0.419, p value = 0.0049) in GSD1b patients (Fig. 1B). No significant changes were observed in the remaining superclusters that included naïve T cells (clusters 2, 4, 5, 10, 16, and 33), memory T cells (8, 11, 14, and 27), naïve B cells (1, 15, 21, and 32), B cells (9, 12, 22, and 23), NKT cells (3), granulocytes (13, 18, 28, and 19) and ILC (29 and 31) (Fig. 1B).
NK and myeloid cell percentage changes in GSD1b are population specific
We then determined if there were significant changes at the cluster level. The analysis of innate cell demonstrated a significant reduction in clusters 6, consisting of anti-inflammatory MΦ, and cluster 17, CD16high monocytes (Fig. 2A). The large decrease in anti-inflammatory MΦ observed may explain the overall decrease in the MΦ & monocyte population described above (Fig. 1B). For the NK populations, cluster 7, consisting of CD16high NK cells, was significantly reduced (fold change GSD1b/control = 0.39, p-value = 0.038, resulting in a global decrease in the number of NK cells, Fig. 1B, Fig. 2A, Fig. 2C). The loss of CD16 expression on NK cells is usually associated with their activation[13] and cluster 7 CD16high NK showed significantly lower CD16 levels in GSD1b patients (fold change GSD1b/control = 0.496, p-value = 0.026), indicative of increased activation of NK cells. However, no relevant or significant increase was observed in CD16low NK clusters. While the overall neutrophil populations were similar between patients and controls, cluster 28, Neutrophil-MDSC, was significantly reduced in GSD1b patients (fold change GSD1b/control = 0.359, p-value = 0.0283, Fig. 2B). Nevertheless, assessment of the neutrophilic compartment after a gradient preparation is of limited value and may not provide an accurate estimation of cell composition.
GSD1b patients exhibit high central memory and low effector memory T cells levels
On the adaptive immunity side, two T cell clusters were altered between GSD1b subjects and controls. Cluster 11, representing central memory T helper 1 cells (cmTh1), was increased (fold change GSD1b/control = 3.54, p-value = 0.015, Fig. 2A), while cluster 27, effector memory cytotoxic T cells (emTc), was reduced in GSD1b patients (fold change GSD1b/control = 0.09, p = 0.043, Fig. 2A), potentially indicating a dysregulated switch from effector memory to central memory T cells. Moreover, the ratios of central memory T cells (clusters 8 and 11, annotation based on: CD45RA– CD45RO+ CCR7+ expression) to effector memory T cells (clusters 14 and 27; annotation based on: CD45RA– CD45RO+ CCR7–expression)[14] in healthy controls and GSD1b was 3.4 times higher in patients with GSD1b, with a confidence interval of 94.61% (p = 0.054, Fig. 2B). Additionally, we observed a trend in the overall reduction of memory T cells and an increase in naïve T cells in the GGD1b subjects with an increase in the ratio of naïve to memory T cells in GSD1b subjects (Fig. 2A, Fig. 2B).
Global downregulation of myeloid markers and upregulation of CXCR3 in GSD1b
To assess differential expression of surface markers between the groups, we evaluated the MMI in all the clusters and plotted changes found significant in Fig. 3A (Supplementary Figure S1B shows all marker fold changes). Although every cluster demonstrated some differences in marker expression between the two groups and almost all markers were altered in at least some of the clusters, we identified a few markers that were consistently downregulated in a majority of clusters among patients with GSD1b, including CD123 (IL-3Rα), CD14 (receptor for lipopolysaccharide-lipopolysaccharide [LPS] binding protein complex), CCR4 (receptor for CCL17 and CCL22), CD24 (ligand of P-selectin, SELP), CD11b (myeloid lineage marker, subunit of integrin CR3) and CD127 (IL-7R). Interestingly, CXCR3 (Receptor for CXCL9, 10, 11), which is involved in trafficking of effector T cells, was significantly upregulated across multiple clusters (Fig. 3B) in GSD1b patients.
In addition, cluster 6, consisting of anti-inflammatory MΦ, exhibited decreased expression of CD163 (fold change GSD1b/control = 0.54, p-value = 0.002, Fig. 3A). CD163 is a cysteine-rich scavenger receptor on monocyte lineage cells involved in immune regulation and tissue homeostasis and has been shown to be strongly downregulated on MΦ and Monocytes in response to proinflammatory signalling[15], which may be consistent with the findings in the GSD1b patients, and may indicate impaired function of this anti-inflammatory macrophage subset. Cluster 27, activated emTc, showed higher expression of CXCR3 (fold change GSD1b/control = 1.78, p-value = 0.01, Fig. 3A), which is considered to represent an activation marker for CD8+ T cells; for this effector memory T cell population, it likely indicates activation and targeting to sites of infection[16]. The largest observed neutrophil population, cluster 18, CD15high-expressing cells, had an increase in MMI for CD45RO (fold change GSD1b/control = 1.763=, p-value = 0.02, Fig. 3A) and a decrease for CD45RA (fold change GSD1b/control = 0.735, p-value = 0.03, Fig. 3A). CD45RO is usually found on non-activated, resting neutrophils, while CD45RA is considered a marker of activation[17], which may suggest that this neutrophil population is less activated in GSD1b patients.