Here we present an adapted protocol that can be used to generate a large number of murine invariant natural killer T cells from mouse spleen. The protocol outlines an approach by which splenic iNKT cells can be enriched for, isolated and expanded in vitro using a limited number of animals and reagents.
The ability to rapidly secrete cytokines upon stimulation is a functional characteristic of the invariant natural killer T (iNKT) cell lineage. iNKT cells are therefore characterized as an innate T cell population capable of activating and steering adaptive immune responses. The development of improved techniques for the culture and expansion of murine iNKT cells facilitates the study of iNKT cell biology in in vitro and in vivo model systems. Here we describe an optimized procedure for the isolation and expansion of murine splenic iNKT cells.
Spleens from C57Bl/6 mice are removed, dissected and strained and the resulting cellular suspension is layered over density gradient media. Following centrifugation, splenic mononuclear cells (MNCs) are collected and CD5-positive (CD5+) lymphocytes are enriched for using magnetic beads. iNKT cells within the CD5+ fraction are subsequently stained with αGalCer-loaded CD1d tetramer and purified by fluorescence activated cell sorting (FACS). FACS sorted iNKT cells are then initially cultured in vitro using a combination of recombinant murine cytokines and plate-bound T cell receptor (TCR) stimuli before being expanded in the presence of murine recombinant IL-7. Using this technique, approximately 108 iNKT cells can be generated within 18-20 days of culture, after which they can be used for functional assays in vitro, or for in vivo transfer experiments in mice.
Murine invariant natural killer T (iNKT) cells are a distinct population of innate T lymphocytes selected in the thymus by CD1d-expressing cortical thymocytes 1,2. iNKT cells express a T cell receptor (TCR) comprised of an invariant Vα14-Jα18 TCR chain paired with either Vβ8, Vβ7 or Vβ2 TCRs 3, which is capable of recognizing endogenous as well as foreign lipid antigens in the context of CD1d. For example, murine iNKT cells recognize and are activated by an endogenous lipid antigen called isoglobotrihexosylceramide (iGb3) 4, as well as α-galactosylceramide (αGalCer) 5,6, a glycolipid isolated from marine sponges. TCR-dependent activation of iNKT cells promotes the priming of adaptive immune responses, and as a result, iNKT cells have been shown to be functionally involved in the amelioration or development of a range of pathologies including rheumatic disease 7 and cancer 8. Currently, synthetic iNKT cell ligands constitute promising new vaccine adjuvants that may be capable of regulating a number of immunopathological conditions.
It has previously been demonstrated that iNKT cells can be generated in vitro following isolation from mouse tissue however; many of these studies employ the use of primary antigen-presenting cells (APCs) and/or cell lines 9, Vα14 TCR transgenic (Tg) mice 10, or thymomas for the generation of iNKT cell-derived hybridomas 11,12. Furthermore, large numbers of mice, high volumes of reagents such as αGalCer-loaded CD1d dimers, and lengthy culture times make some published protocols less ethically and economically appealing 9,13.
In this report we describe an adapted method for the isolation and in vitro expansion of iNKT cells from mouse spleen. More specifically, the protocol describes a method for enriching iNKT cells from mouse spleen which reduces the mice, reagents and time required for FACS cell sorting, and proposes an optimized approach for expanding sorted splenic iNKT cells in vitro.
In this study, adult (6-8 weeks) female C57Bl/6 mice were used. Mice were housed and bred according to the guidelines of the Ghent University vivarium. All animal procedures were approved by the Institutional Animal Care and Ethics Committee.
1. Preparation of Mononuclear Cells (MNCs) from Mouse Spleen
2. Enrichment, Detection and Purification of Mouse iNKT Cells
3. Culture and Expansion of Mouse iNKT Cells
Day 0
Day 2
Day 4
Day 8
Day 11 – 18
Day 19-20
4. Cytokine Production by Mouse iNKT Cells Using a CD1d Plate-bound Assay
Isolation of splenic mononuclear cells using a density gradient takes approximately 1 hr and eliminates the use of reagents required to lyse red blood cells (RBCs). A high yield of viable cells is obtained using this method and debris generated during straining of the organ is removed. Typically, the frequency of iNKT cells within the splenic lymphocyte pool ranges between 1 and 5% of total T lymphocytes however, this can vary depending on the age, sex and health status of the animals used. Approximately 106 iNKT cells can be acquired from the pooled spleens of 3 mice and the highest yield of iNKT cells are obtained from spleens of 6-8 week old mice.
The use of mouse anti-CD5 magnetic beads significantly enriches for iNKT cells within the splenic MNC fraction and, apart from a minor population of B lymphocytes that express the CD5 antigen, the majority of cells isolated using this procedure constitute CD5+ lymphocytes. For example, 5-8% of the MNCs obtained after CD5 enrichment are CD5-negative (Figure 1H). For iNKT cell FACS sorting, combining αGalCer/CD1d tetramer and anti-mouse CD3ε yields iNKT cell purities above 98% however, FACS dump channels for splenic B and CD8 T cells should be used to eliminate ‘sticky’ lymphocyte populations during the sort. In addition, gate out any doublets that may have formed during the CD5 enrichment step. Using this FACS setup, we obtained iNKT cell purities post-sort in the order of 99% (Figure 2H).
Stimulating 106 sorted iNKT cells with plate-bound anti-CD3ε in the presence of IL-2, IL-12 and soluble anti-CD28 resulted in a 3-fold expansion of iNKT numbers following 2 days of culture (Figure 3). Subsequent expansion iNKT cells in the presence of IL-7 results in a 3- to 4-fold increase in the number of iNKT cells present at day 4 in culture. Notably, repeating these culturing conditions can yield an average of 7 x 107 iNKT cells after two rounds of expansion without any visible loss of cells between changes in culture media on different days (Figure 3). Thus, murine splenic iNKT cells can be expanded at least 70-fold using these conditions in 18 days.
We also assessed the cytokine producing capacity of expanded iNKT cells by stimulation with plate-bound recombinant murine CD1d loaded with αGalCer. At 48 hr post-stimulation, IL-2, IL-4, IFN-γ, TNF-α and IL-6 could be readily detected in culture supernatants by ELISA (Figure 4). Expanded iNKT cells therefore retain the ability to produce Th1 and Th2 cytokines post-expansion.
Figure 1. Enrichment for CD5+ lymphocytes from mouse splenic MNCs. Gating strategy for analyzing the percentage of CD5+ lymphocytes present in pre-enriched (A-D) and magnetic cell separation-enriched (E-H) mouse splenic MNC suspensions. Cell doublets (A, E) and dead cells (B, F) have been excluded using FSC-H versus FCS-W and DAPI versus FSC-A plots, respectively. The percentage CD5+ cells present within the lymphocyte gate (C, G) both before and after enrichment are shown in D and H, respectively. Please click here to view a larger version of this figure.
Figure 2. FACS sorting iNKT cells from CD5-enriched splenic MNCs. Gating strategy for analyzing the percentage αGalCer/CD1d tetramer+CD3ε+ iNKT cells present before (A–D) and after (E–H) FACS sorting. The gating strategy eliminates cell doublets (A, E), dead cells and CD8+CD19+ lymphocytes (B, F) from the analysis by plotting FSC-H versus FCS-W and DAPI, CD8 and CD19 (dump channel) versus FSC-A, respectively. The percentage αGalCer/CD1d tetramer+CD3ε+ iNKT cells present within the lymphocyte gate (C, G) before and after FACS sorting are shown in (D) and (H), respectively. CD1d-Tet., αGalCer/CD1d Tetramer. Please click here to view a larger version of this figure.
Figure 3. Absolute number of iNKT cells generated in vitro. Fold increase in the number of iNKT cells at the indicated time points after 3 weeks of expansion in vitro. Please click here to view a larger version of this figure.
Figure 4. Cytokine producing capacity of in vitro expanded iNKT cells. Day 20 expanded iNKT cells were stimulated in vitro with mouse αGalCer-loaded CD1d. After 72 hr supernatants were collected and analyzed for the presence of IFN-γ, IL-4, TNF-α, IL-2 and IL-6 by ELISA. Bars represent means SEM (n = 2). Please click here to view a larger version of this figure.
Critical steps in the current protocol include the isolation and subsequent enrichment of CD5+ lymphocytes (Section 1 & 2), FACS sorting (Section 3) and the initial plating of iNKT cells (Section 4). Of the steps performed in Section 1, remember to carefully layer the splenic cellular suspension over the density gradient medium such that a distinct cellular interphase is generated following centrifugation. The subsequent enrichment for CD5+ lymphocytes by magnetic cell separation (Section 2) minimizes the reagents and time required to stain for and FACS sort iNKT cells (Section 3), which helps increase iNKT cell yields post-sort. Finally, it is important to seed no more than 105 iNKT cells per well for the first 2 days of culture (Section 4) as seeding wells with higher numbers of iNKT cells can result in cellular apoptosis.
A number of considerations are important when modifying and/or troubleshooting this protocol: Firstly, the age of the animals used is important. Animals that are either too old, or have accessory infections, may hamper your ability to isolate, distinguish, and FACS sort sufficient cells from the spleen. Secondly, when staining with αGalCer/CD1d tetramers, it is important to keep the volume of cells resuspended in PBS buffer low as too high a volume dilutes out the staining efficiency of the αGalCer/CD1d tetramer, which in turn reduces the clustering of tetramer+ iNKT cells by FACS. Ideally, the presence of tightly clustered αGalCer/CD1d tetramer+ iNKT cells during FACS acquisition allows for more accurate gating by FACS and yields higher percentage purity iNKTs during post-sort analysis. This is important as lower sorted iNKT cell yields will result in the outgrowth of other contaminating T cell populations during culture. Thirdly, continuously refresh medium that becomes yellow during the culture and expansion of iNKT cells. For example, replace 50% of yellowed medium with new medium containing the appropriate cytokines, particularly during days 8 and day 11 of culture. iNKT cell yields can be maximized in this way.
To our knowledge this is the first iNKT expansion protocol to include a density gradient and CD5+ lymphocyte enrichment step for the isolation and enrichment of iNKT cells from mouse spleen. A number of alternative approaches have been explored to enrich for splenic iNKT cells including αGalCer/CD1d dimers 13, Vα14 TCR Tg mice 10 as well as depletion of non-T cells by magnetic cell separation 9. However, although iNKT cells can be successfully expanded in vitro using these approaches, such methods require either large volumes of αGalCer/CD1d dimers to enrich for iNKTs 13, only generate transgenic iNKT cells 10, or simultaneously give rise to some non-iNKT cell lines 9. Furthermore, the use of plate-bound anti-CD3ε to maintain and expand sorted iNKT cells (Section 4) precludes a requirement for activated APCs during iNKT expansion in vitro 9. In this context, an APC-free iNKT expansion protocol has the advantage of not having to separate APCs from expanded iNKT cells prior to injection in vivo. We should however also add that the protocol described is limited by the fact that the investigator requires easy access to, as well as the relevant training, to calibrate and operate a FACS sorter. Unfortunately FACS sorters are expensive and they are not always available in every laboratory. Nevertheless, although the current protocol has been optimized to isolate and culture murine iNKT cells, the enrichment steps described herein can also be used to isolate and study iNKT recent thymic emigrants (RTEs) 16 and can be adapted to enrich for and characterize other rare T cell populations by FACS.
Collectively, we define an optimized approach that can be used to efficiently generate up to 108 iNKT cells from the spleens of three mice within 3 weeks. iNKT cells generated in this manner retain the ability to secrete cytokines upon stimulation, making them useful for adoptive transfer experiments and the study of iNKT cell biology in vivo.
The authors have nothing to disclose.
D.E. and M.B.D. are members of a multidisciplinary research platform (MRP) of Ghent University, and the Ghent Researchers on Unfolded Proteins in Inflammatory Disease (GROUP-ID) consortium.
Material | |||
recombinant murine IL-2 | eBiosciences | 14-8021 | |
recombinant murine IL-12 | eBiosciences | 39-8122-65 | |
recombinant murine IL-7 | eBiosciences | 14-8071 | |
purified anti-mouse CD3e (145-2C11) | eBiosciences | 16-0032-86 | |
purified anti-mouse CD28 (37.51) | eBiosciences | 16-0281-85 | |
e450-conjugated anti-mouse CD19 (eBio1D3) | eBiosciences | 48-0193-82 | |
e450-conjugated anti-mouse CD8α (53-6.7) | eBiosciences | 48-0081-82 | |
FITC-conjugated anti-mouse CD5 (53-7.3) | eBiosciences | 11-0051-81 | |
V500-conjugated anti-mouse CD3ε (500A2) | BD biosciences | 560771 | |
anti-mouse CD5 (Ly-1) microbeads | Macs Miltenyi Biotec | 130-049-301 | |
purified anti-mouse CD16/32 (2.4G2) | Macs Miltenyi Biotec | 130-092-575 | |
MACS MS Columns | Macs Miltenyi Biotec | 130-042-201 | |
Trypan Blue, 0.4% (wt/vol) | Gibco | 15250-061 | |
RPMI 1640 medium | Gibco | 12633-020 | |
1x PBS | Gibco | 10010-056 | [Ca2+/Mg2+ – free] |
Fetal calf serum | Gibco | 10270 | |
L-Glutamine | Gibco | 25030-123 | |
Penicillin-streptomycin | Sigma-Aldrich | P4458-100ML | |
Bovine serum albumin | Sigma-Aldrich | A7906-100MG | |
β-Mercaptoethanol | Sigma-Aldrich | M3148 | |
Ethylenediaminetetraacetic acid | Sigma-Aldrich | EDS-1KG | |
Ficoll-Paque plus | GE Healthcare | 71-7167-00 AF | |
Equipment | |||
96-well plate F-bottom | Greiner-bio one | 657-160 | |
24-well plate | Greiner-bio one | 665-180 | |
6-well plate | Greiner-bio one | 655-180 | |
15 ml falcon tube | Greiner-bio one | 188-271 | |
50 ml falcon tube | Greiner-bio one | 227-261 | |
70 µm filter | Greiner-bio one | 542-070 | |
30 µm filter | Millipore | SVGP01050 | |
MiniMACS separator | Macs Miltenyi Biotec | 130-042-102 | |
MS Columns | Macs Miltenyi Biotec | 130-042-201 | |
Water-jacketed CO2 incubator | VWR | ||
Hemocytometer | VWR | ||
Dissection Kit | VWR | ||
BD FACSAria III | BD Biosciences |