6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

OF THE SECURITIES EXCHANGE ACT OF 1934

For the Month of September, 2015

Commission File Number: 001-37368

ADAPTIMMUNE THERAPEUTICS PLC

(Translation of registrant’s name into English)

101 Park Drive, Milton Park
Abingdon, Oxfordshire OX14 4RY
United Kingdom

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F x Form 40-F  o

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):

Yes o No  o

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):

Yes o No  o

Other Events

On September 14, 2015, Adaptimmune Therapeutics plc (the “Company”) issued a press release announcing that on September 17, 2015, James Noble, the Company’s Chief Executive Officer, will be presenting at the 2015 Morgan Stanley Global Healthcare Conference and Dr. Helen Tayton-Martin, the Company’s Chief Operating Officer, will be presenting at the 2015 Bank of America Merrill Lynch Global Healthcare Conference. The press release is attached as Exhibit 99.1 and the presentation to be given at the 2015 Morgan Stanley Global Healthcare Conference is attached as Exhibit 99.2 and both exhibits are incorporated by reference herein. A shortened version of Exhibit 99.2 will be presented at the 2015 Bank of America Merrill Lynch Global Healthcare Conference.

Exhibits

99.1Press release dated September 14, 2015

99.2 Presentation materials dated September 2015

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

	Adaptimmune Therapeutics plc
	By:	/s/ Margaret Henry
	Name:	Margaret Henry
	Title:	Corporate Secretary
Date: September 15, 2015

3

EX-99.1

Exhibit 99.1

Adaptimmune to Participate in Two Upcoming Investor Conferences

PHILADELPHIA, Pa. and OXFORD, UK., September 14, 2015 — Adaptimmune Therapeutics plc (Nasdaq: ADAP), (“Adaptimmune” or the “Company”), a clinical stage biopharmaceutical company focused on the use of T-cell therapy to treat cancer, today announced participation in the following two investor conferences:

James Noble, Chief Executive Officer of Adaptimmune, will present at the 2015 Morgan Stanley Global Healthcare Conference at 4:05 PM ET (9:05 PM BST) on Thursday, September 17, 2015. The conference is being held at the Grand Hyatt New York in New York City.

Dr. Helen Tayton-Martin, Chief Operating Officer of Adaptimmune, will present at the 2015 Bank of America Merrill Lynch Global Healthcare Conference at 9:00 AM BST (4:00 AM ET) on Thursday September 17, 2015. The conference is being held at the Bank of America Merrill Lynch Financial Centre in London, UK.

Adaptimmune’s presentations will be webcast live for investors through the investor section of www.adaptimmune.com and available for a period of 30 days following the conference.

About Adaptimmune

Adaptimmune is a clinical stage biopharmaceutical company focused on novel cancer immunotherapy products based on its T-cell receptor platform.  Established in 2008, the Company aims to utilize the body’s own machinery — the T-cell — to target and destroy cancer cells by using engineered, increased affinity T-cell receptors (TCRs) as a means of strengthening natural patient T-cell responses. Adaptimmune’s lead program is an affinity enhanced TCR therapeutic targeting the NY-ESO cancer antigen. Its NY-ESO TCR therapeutic candidate has demonstrated signs of efficacy and tolerability in Phase 1/2 trials in solid tumors and in hematologic cancer types. In June 2014, Adaptimmune announced that it had entered into a strategic collaboration and licensing agreement with GlaxoSmithKline (GSK) for the development and commercialization of the NY-ESO TCR program in partnership with GSK.  In addition, Adaptimmune has a number of proprietary programs and its next TCR therapeutic candidate, directed at MAGE A-10, is scheduled to enter the clinic in 2015. The Company has identified over 30 intracellular target peptides preferentially expressed in cancer cells and is currently progressing eight of these through unpartnered research programs.  Adaptimmune has over 150 employees and is located in Oxfordshire, UK and Philadelphia, USA.  For more information:  http://www.adaptimmune.com

Adaptimmune Contacts

Will Roberts

Vice President, Investor Relations

T:  (215) 966-6264

E: will.roberts@adaptimmune.com

Margaret Henry

Head of PR

T: +44 (0)1235 430036

Mob: +44 (0)7710 304249

E: margaret.henry@adaptimmune.com

EX-99.2

Exhibit 99.2

Adaptimmune Engineered TCR T cell therapy Presentation Materials September 2015

Disclaimer This presentation contains “forward-looking statements,” as that term is defined under the Private Securities Litigation Reform Act of 1995 (PSLRA), which statements may be identified by words such as “believe,” “may”, “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect” and other words of similar meaning. These forward-looking statements involve certain risks and uncertainties. Such risks and uncertainties could cause our actual results to differ materially from those indicated by such forward-looking statements, and include, without limitation: the success, cost and timing of our product development activities and clinical trials; our ability to submit an IND and successfully advance our technology platform to improve the safety and effectiveness of our existing TCR therapeutic candidates; the rate and degree of market acceptance of T-cell therapy generally and of our TCR therapeutic candidates; government regulation and approval, including, but not limited to, the expected regulatory approval timelines for TCR therapeutic candidates; and our ability to protect our proprietary technology and enforce our intellectual property rights; amongst others. For a further description of the risks and uncertainties that could cause our actual results to differ materially from those expressed in these forward-looking statements, as well as risks relating to our business in general, we refer you to our final Prospectus filed with the Securities and Exchange Commission on May 7, 2015. We urge you to consider these factors carefully in evaluating the forward-looking statements herein and are cautioned not to place undue reliance on such forward-looking statements, which are qualified in their entirety by this cautionary statement. The forward-looking statements contained in this presentation speak only as of the date the statements were made and we do not undertake any obligation to update such forward-looking statements to reflect subsequent events or circumstances. We intend that all forward-looking statements be subject to the safe-harbor provisions of the PSLRA.

Investment Highlights Focused on engineered T cell receptors (TCR) for autologous T cell therapeutics to treat cancer Lead clinical candidate, NY-ESO T-cell therapeutic, is in multiple human studies and has shown efficacy in solid tumours and haematologic cancer types Synovial sarcoma – 6 responses seen in first 10 patients (1 CR, 5 PRs) Multiple myeloma in ASCT setting – 59% nCR/CR rate IND for next TCR programme approved, patients enrolling late 2015 (MAGE A10) Strategic collaboration with GSK - up to $350mm in milestones over 7 years, initially focused on NY-ESO NASDAQ Listing (ADAP) 70.8 million ADSs outstanding (1 ADS : 6 Shares) Post-IPO Cash ~ $300 million

TCR Platform built up over 15 years 1999-2006 Avidex formed on basis of TCR technology from Oxford University Acquired by Medigene (2006) 2008 Adaptimmune formed as a virtual company with UPenn collaboration 2011-2014 Adaptimmune establishes R&D infrastructure and delivers promising clinical data 2014 Strategic collaboration with GSK + $104m Series A Funding Round 2015 IPO on Nasdaq (ADAP) Net proceeds ~$176m PHILADELPHIA ( ~35 FTEs ) OXFORD ( ~128 FTEs )

Experienced Management Team and Board Executive Management Name: Title: Experience: James Noble, MA, FCA CEO & Co-Founder Helen Tayton-Martin, PhD MBA COO & Co-Founder Adrian Rawcliffe CFO Rafael Amado, MD CMO Gwen Binder-Scholl, PhD EVP, Adaptimmune LLC Board of Directors Name: Affiliation: Experience: Jonathan Knowles, PhD, Chairman Independent James Noble, MA, FCA CEO & Co-Founder David Mott NEA Ali Behbahani, MD NEA Peter Thompson, MD OrbiMed Elliott Sigal, PhD NEA Ian Laing Independent Larry Alleva Independent Institutional Investors

TCRs recognise intracellular cancer antigens The TCR is the natural mechanism for T cells to distinguish a diseased cell from a healthy cell All proteins, including intracellular ones, are processed and presented as HLA-peptide complexes which are recognized by TCRs Many cancer targets are intracellular – TCR therapeutics can access these targets

Autologous T cell therapy Blood is taken from a patient, including cells from the immune system Adaptimmune modifies cells from the immune system with enhanced T cell receptors (TCRs) The cells are grown and re-infused to the patient The engineered cells then find and destroy cancer cells Patient Apheresis Patient Screening GMP T Cell Engineering GMP T Cell Expansion Release Testing Patient Infusion

NY-ESO TCR MAGE A10 TCR 12 Research Programs 20+ Validated Targets NSCLC Other solid tumors TCR Candidate Rights Research Pre-IND Phase 1/2 Comments First cohort completed Two further cohorts enrolling 1st trial published in NMED 2nd trial (no auto SCT) in 2016 Continuing enrollment Initiating in 2015 IND open Breast, GI, Bladder, H&N under consideration Wholly-owned internal programs: multiple INDs 2017 onward in multiple cancer indications Hepatocellular cancer AFP TCR Completing pre-clinical safety assessment Adaptimmune GSK option to license ADAP Pipeline: Robust Pipeline of T-Cell Receptors Synovial Sarcoma Multiple myeloma (w/ and w/o auto-SCT) Ovarian, Melanoma NSCLC GSK Collaboration Worldwide Worldwide Worldwide Worldwide Esophageal Investigator-initiated study paused* * Investigators carrying out study have voluntarily suspended patient recruitment pending investigation of a patient death occurring 46 days after T-cell infusion.

Large un-partnered pipeline with ability to target almost all major tumors Adaptimmune GSK 20+ Additional validated targets Twelve new targets selected for development Not yet nominated; programs with work ongoing are excluded Pool of 3: ADAP keeps 2 NY-ESO MAGE-A10 AFP 30+ validated therapeutic targets preferentially expressed in cancer cells

Key 2015/2016 Milestones YTD and Anticipated Q1 2015 Additions to Adaptimmune senior leadership team April 2015 AACR presented full cohort data for NY-ESO in Sarcoma and MM May 2015 IPO raises $176m net proceeds Q2 2015 Filing and acceptance of IND for Phase 1/2 studies for MAGE A-10 Q3 2015 Publication of Nature Medicine paper Q3 2015 Initiation of further NY-ESO cohorts in sarcoma 2H 2015 NSCLC study to open with NY-ESO 2H 2015 Initiation of Phase 1/2 studies for MAGE A-10 2016 Additional Phase 1/2 data from NY-ESO clinical studies in: Sarcoma Ovarian Lung Melanoma Myeloma 2016 Initiation of AFP in hepatocellular cancer 2H 2016 First data on MAGE A10 studies 2016 + INDs for multiple additional TCR therapeutic candidates 2015 2016

Platform and Differentiation

Adaptimmune: The Leader in TCR T-cell Therapy Proprietary Technology TCR Engineering Safety Testing Robust Manufacturing Target Validation TCR Gene Delivery T-Cell Isolation T-Cell Expansion Multiple, soluble TCRs Potent and specific Enhanced TCRs Enhanced TCRs Molecular analysis Human Cell testing Clinical Candidate >30 low risk targets selected for TCR program No/low expression on normal tissue Frequency of expression across multiple tumors Expression on tumor cells

Integrated TCR Discovery and Development Platform Enables ADAP to identify real cancer targets and to engineer and develop T-cell therapeutics against those targets Protected by a combination of patents and know-how Highly differentiated among peers 7. In house R&D and IP 1. Target identification and validation 2. Making TCRs 3. Engineering TCRs 4. Preclinical and safety testing 5. Manufacturing 6. Clinical and regulatory

NY-ESO in Synovial Sarcoma

Synovial Sarcoma Develops from soft tissues such as muscle, or deep skin tissues Generally incurable - 75% to 80% of patients do not survive past two to three years First line therapy - radiotherapy and chemotherapy, surgical resection where possible FDA granted approval for marketing of Votrient® (pazopanib hydrochloride) for treatment of soft tissue sarcoma in patients who had received prior chemotherapy (2012) Progression-free survival for synovial sarcoma patients was 4.1 months (placebo = 0.9 months) Across all soft tissue sarcomas, 11 partial responses, 0 complete responses

ADAP Phase I/II Study in Synovial Sarcoma Multicenter pilot study in 11 patients Objectives include Determine the response rate following NY-ESO-1 Specific T cells Persistence and expansion of engineered T-cells and correlate this with clinical response Patients conditioned with high-dose fludarabine and cyclophosphamide followed two days later by NY-ESO T-cell infusion Fludarabine Cyclophosphamide -5 -4 -3 -2 -1 0 NY-ESO T Cells (1 billion cells / kg; max 40 billion) 7 30 60 90 Day on Study Response Assessments

Synovial Sarcoma : Encouraging Response Rate, Tolerability and Persistence Of the first 10 patients, six responded: only T-cell technology to show clinical anti-tumor response in a solid tumor One complete response, four partial responses, one response at one month Two non responders potentially under-dosed Generally well tolerated Fever and cytokine release common in week following infusion (Grade 1 to 3, none with CNS) Evidence of pseudo-progression and gradual reductions in tumor burden with evidence of NY-ESO TCR+ T-cells in resected tumor Expansion of T-cells and ongoing responses occurred without high dose IL-2 administration Persistence of engineered T-cells out to one year following cell infusion

***Surgical resection of primary but still with PR of lung lesions ** Progression of disease from nadir or CR resection of NY-ESO+ lung mets # Low cell dose, late cytokine release syndrome with tumor infiltrating NY-ESO-1+ cells, tumor progression Synovial Sarcoma : Reduction in tumour volume % Change from Baseline (Sum of diameters in target lesions) Months from Cell Infusion -100 -75 -50 -25 0 25 50 75 0 1 2 3 4 5 6 7 8 9 200 201 202 204 205 261 206 207 208 263

ADAP Phase I/II Study in Synovial Sarcoma Radiographic Pseudoprogression and Response of Lung Metastases Baseline: Bilateral Miliary Metastatic disease Day +2: Pseudoprogression due to Immune Infilration Day +101: Complete Response Patient 201 NY-ESO C-Reactive Protein AACR April 2015

NY-ESO TCR T cells administered ADAP Phase I/II Study in Synovial Sarcoma Partial Response Followed by Tumor Resection in Sarcoma One month post NY-ESO TCR T cells Two months post NY-ESO T cells Source: Merchant, CTOS, 2014 ~ 70% reduction in lesion size at 2 months after administration of NY-ESO T-cells The lesion was then deemed capable of resection

NY-ESO in Multiple Myeloma

Multiple Myeloma Formed by malignant plasma cells in bone marrow US prevalence: 77,600 cases - approximately 27,000 new cases expected in 2015 Average five-year survival rates are estimated to be less than 45 percent Majority of patients treated with chemotherapy eventually relapse and cannot be further treated Median survival is six to nine months at this stage

ADAP Phase I/II Study in Multiple Myeloma Study Design All enrolled patients (n=25) had symptomatic myeloma with active disease High risk population Average of 3 prior Rx Five patients had prior autologous stem cell transplant 12 with cytogenetic abnormalities, including seven categorized as high-risk Patients conditioned with high-dose melphalan followed two days later by ASCT Stem Cells High dose melphalan -2 0 +2 NY-ESO T Cells (1-10 billion total cells) 42 100 180 270 Day on Study Response Assessments (marrow / myeloma markers)

ADAP Phase I/II Study in Multiple Myeloma Compelling Response Rate Compared to Published Literature Two year overall survival (OS) and progression free survival (PFS) as of April 2015 16/25 patients remain alive; 8/25 remain in remission Median PFS = 19.1 months Median OS = 32.1 months 59 percent (13/22) response rate (RR: CR + NCR); 90 percent Overall Response Rate (ORR: VGPR/nCR/CR/PR) Percent of Patients with nCR/CR NY-ESO T cell Response Rate at Day 100 Compared to Historical Published Data 24% 38% 59% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Transplant only* Transplant + Bortezomib* Adaptimmune NY-ESO T cells + Transplant

ADAP Phase I/II Study in Multiple Myeloma Encouraging Tolerability and Persistence Generally well tolerated - all SAEs possibly related to the NY-ESO T-cells resolved No clinically apparent cytokine release syndrome despite high IL-6 levels CAR-Ts have been associated with severe adverse events attributable in part to grade 3 or 4 cytokine release syndrome No need for high dose IL-2 to support engineered T-cell persistence Prolonged persistence and trafficking of cells detected - cells persist >6 months in most patients Infused cells remain functional, without exhaustion, and include a diversity of phenotypes

MAGE A10 Next proprietary target

IND for MAGE A-10 TCR therapeutic filed Preclinical testing complete NIH RAC approval obtained – March 10, 2015 IND approved – announced July 2, 2015 Initial trial in NSCLC expected to open in 2015 Further indications under consideration: Bladder, Head and Neck, Breast and GI cancers

The GSK Strategic Collaboration Announced June 2014 – Up-front payment £25M GSK has option to license NY-ESO at end of Phase 1/2 studies Adaptimmune conducts all clinical and non-clinical development work Enables Adaptimmune to optimize regulatory, vector, cell processing, analytical, automation, diagnostic, cell improvements, etc GSK can nominate up to four other targets, but not MAGE A-10 or the designated targets in our ongoing research programs Up to $350 million in funding and milestones in first seven years Covers milestones for 3 of 5 targets; assuming 2 have MAs filed in US and EU Four milestones already reached Royalties (mid-single to low double digit) and sales milestones payable

Adaptimmune (NASDAQ: ADAP) Clinical stage biopharmaceutical company located in Oxfordshire, UK and Philadelphia, PA Well capitalized with 70.8M shares outstanding: ~$300M pro forma cash in F1 Developing engineered T-cell receptors (TCRs) to target cancer cells which the natural immune system cannot detect Highly differentiated among immuno-oncology peers due to proprietary integrated technology platform for TCR discovery, engineering and development Lead clinical candidate (NY-ESO) has demonstrated tolerability and efficacy in solid tumours and haematologic cancer types IND for newest TCR programme (MAGE A10) accepted by FDA - enrollment to begin in 2015 Anticipate multiple INDs per year from 2016 onwards

Adaptimmune Engineered TCR T cell therapy Presentation Materials September 2015