Exhibit 99.1 Company Presentation May 2026

Forward-Looking Statements This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. These statements may be identified by words such as “aims,” “anticipates,” “believes,” “could,” “estimates,” “expects,” “forecasts,” “goal,” “intends,” “may,” “plans,” “possible,” “potential,” “seeks,” “will,” and variations of these words or similar expressions that are intended to identify forward-looking statements. Any such statements in this presentation that are not statements of historical fact may be deemed to be forward- looking statements. These forward-looking statements include, without limitation, statements regarding the potential of our EDO platform to deliver high levels of oligonucleotide to the nuclei, the promising trends and therapeutic potential and safety profile of PGN-EDODM1 based on data from the 5, 10 and 15 mg/kg cohorts of the FREEDOM study and 5 mg/kg cohort of the FREEDOM2 study, our expectations regarding the potential for significant correction of mis-splicing with more and higher doses of PGN-EDODM1 over a longer treatment period to potentially provide improved functional benefit for patients with DM1, the design, initiation and conduct of clinical trials, including expected timelines for data readouts from our FREEDOM2 trial, the potential for any functional improvements that may result from robust splicing correction with PGN-EDODM1, dose-dependent increases in splicing suggesting that PGN-EDODM1 is getting into the muscle and effectively binding to the target, the potential for PGN-EDODM1 to offer a best-in-class treatment option, ongoing and planned regulatory interactions and our financial resources and expected cash runway. Any forward-looking statements in this presentation are based on current expectations, estimates and projections only as of the date of this presentation and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to: delays or failure to successfully initiate or complete our ongoing and planned development activities for our product candidates, including PGN-EDODM1; our ability to enroll patients in our clinical trials, including FREEDOM2, that our interpretation of clinical and preclinical study results may be incorrect, or that we may not observe the levels of therapeutic activity in clinical testing that we anticipate based on prior clinical or preclinical results, including for PGN-EDODM1; our product candidates, including PGN-EDODM1, may not be safe and effective or otherwise demonstrate safety and efficacy in our clinical trials; adverse outcomes from our regulatory interactions, including delays in regulatory review, clearance to proceed or approval by regulatory authorities with respect to our programs, including clearance to commence planned clinical studies of our product candidates, including release of the partial clinical hold placed by FDA on the FREEDOM2 study, or other regulatory feedback requiring modifications to our development programs, including with respect to the FREEDOM2 program; changes in regulatory framework that are out of our control; our ability to obtain, maintain and protect our intellectual property; our ability to enforce our patents against infringers and defend our patent portfolio against challenges from third parties; competition from others developing therapies for the indications we are pursuing; unexpected increases in the expenses associated with our development activities or other events that adversely impact our financial resources and cash runway; and our dependence on third parties for some or all aspects of our product manufacturing, research and preclinical and clinical testing. Additional risks concerning PepGen's programs and operations are described in our most recent filings with the SEC. PepGen explicitly disclaims any obligation to update any forward-looking statements except to the extent required by law. This presentation discusses PGN-EDODM1, an investigational therapy, that has not been approved for use in any country, and is not intended to convey conclusions about their efficacy or safety. There is no guarantee that PGN-EDODM1 or any other investigational therapy will successfully complete clinical development or gain regulatory authority approval. 2

Leveraging EDO Platform to Drive Meaningful Impact for Patients PGN-EDODM1: Myotonic Dystrophy Type 1 OUR VISION • Best-in-class potential; selectively targets only pathogenic DMPK RNA • Favorable emerging safety profile and FREEDOM2 5mg/kg results Develop therapies that address supportive of the ongoing dosing in 10 mg/kg MAD cohort • FREEDOM2 cleared in South Korea, Australia, and New Zealand; the root cause of serious EDO PLATFORM enrollment open and active in Canada, UK, and South Korea genetic neuromuscular and • Orphan Drug & Fast Track Designation (U.S.); Orphan Designation (EU) neurological diseases—driving Achieving superior meaningful, functional improvement nuclear delivery and Anticipated Upcoming Milestones Backed by a team of leading uptake of therapeutic • 2H 2026: FREEDOM2 10 mg/kg clinical results oligonucleotides, • 2027: FREEDOM2 12.5 mg/kg clinical results neuromuscular researchers overcoming key limitations with deep expertise in genetic disease biology and oligonucleotide of prior approaches drug development Research Pipeline Strong cash runway into 2H 2027, • Developing research pipeline that applies platform differentiators to address underlying neuromuscular disease drivers through FREEDOM2 12.5 mg/kg • Exploring EDO's potential in genetic conditions, including Charcot- MAD readout Marie-Tooth disease 3

PepGen’s EDO Platform Has Been Designed and Developed to Solve the Delivery Challenge of Oligonucleotides PGN-EDODM1 Delivery to DM1 Patient Myotubes EDO platform results in nuclear delivery of oligonucleotide Red = oligo therapeutics Immortalized myoblasts from a DM1 patient with 2600 CTG repeats were cultured then differentiated for 4 days into myotubes and then treated with fluorescently tagged 4 PGN-PMODM1 (PMO) or PGN-EDODM1 (PPMO) at 10 uM. Cells were visualized by confocal microscopy 24h after treatment.

EDO Technology Can Improve Endosomal Escape and Has Been Shown to Increase Nuclear Uptake up to 98-Fold PMO Delivery in DM1 Cells 73x NUCLEAR UPTAKE 2.0 1.5 98x 1.0 55x 0.5 0.0 1 5 10 20 Concentration (nmol) Immortalized myoblasts from a healthy individual or a DM1 patient with 2600 CTG repeats were cultured then differentiated for 4 days into myotubes and then treated with fluorescently tagged PGN-PMODM1 (PMO) or PGN-EDODM1 (PPMO) at concentrations detailed above. Cells were visualized by confocal 5 microscopy 24h after treatment. Graphs are presented as mean ± SD. Nuclear uptake (pmol)

PGN-EDODM1: A Differentiated Drug with Best-in-Class Potential 1 Differentiated Delivery Technology • Receptor-independent EDO peptide delivery • Designed to escape the endosome – unlike TfnR targeting 2 Differentiated Target • Selectively targets pathogenic RNA (CUG repeat in DMPK) 1 • Demonstrated highest rate of splicing correction ever reported in DM1 after a single dose 3 Cost Effective Manufacturing • EDO peptide is a short linear peptide – not cell culture product 1. FREEDOM 15 mg/kg data readout when compared with prior published data. 6

PGN-EDODM1 – Myotonic Dystrophy Type 1 (DM1)

Myotonic Dystrophy Type 1 Overview and Unmet Medical Need Overview Market Opportunity Jubal, retired professor living with DM1 • CUG expansion in the DMPK • U.S. and EU over 115,000 gene patients • Onset of symptoms variable- • No approved therapies that childhood to adulthood address underlying cause of the disease – Myotonia – Muscle weakness – Cardiac arrythmias – Loss of lung function – Fatigue • Average life expectancy is 50-60 years for non- congenital forms of DM1 Sources: Neuroepidemiology (2022) 56 (3): 163–173., Neurology 2021 Feb 16;96(7):e1045-e1053 8 CUG: cytosine-uracil-guanine; DMPK: dystrophia myotonica protein kinase

exp PGN-EDODM1 Blocking Approach Targets the Pathogenic CUG Repeats DMPK RNA PGN-EDODM1 binds selectively to the pathogenic DM1 is caused by pathogenic DMPK transcripts DMPK transcript Trapped Liberated MBNL1 is MBNL1 inactive and restores correct results in splicing mis-splicing exp • DM1 is caused by pathogenic DMPK transcripts containing CUG • PGN-EDODM1 binds selectively to the pathogenic DMPK transcript repeat sequences that form hairpin loops exp • This reduces the ability of the CUG repeats to form hairpin loops • These hairpin loops trap MBNL1 proteins that are needed for and sequester RNA splicing proteins correct splicing of mRNAs DMPK transcript Bound MBNL1 (inactive) PGN-EDODM1 Free MBNL1 (active) 9 Wojciechowska, et al., Quantitative Methods to Monitor RNA Biomarkers in Myotonic Dystrophy, Nature, April 12, 2018

PGN-EDODM1 Reduced Pathogenic Nuclear Foci, Liberated MBNL1 and Corrected Mis-Splicing in Patient Cells with Long CUG Repeats Foci Reduction MBNL1 Liberation Mis-Splicing Correction Not Treated Not Treated Across multiple transcripts 69% correction 54% reduction in PGN-EDODM1 Treated PGN-EDODM1 Treated toxic foci Immortalized myoblasts from healthy individual or DM1 patient with 2600 CTG repeats were cultured then differentiated for 4 days into myotubes. Treatment with peptide-PMO conjugates at concentrations given. Cells were harvested for analysis 24h after treatment. RNA isolation, RT-PCR and capillary electrophoresis (QIAxcel) analysis were performed. 10 Visualization with FISH and immunofluorescence microscopy. Mean ± SD; n = 5 per group.

Multiple Doses of PGN-EDODM1 Led to Greater Improvement in Splicing Correction and Myotonia vs Single Dose in Preclinical Studies Tissue Concentration Mis-Splicing Correction Correction of Myotonia Skeletal muscle Across multiple transcripts Pinch test 99% 120 68% 56 Correction of 76% myotonia 0 0% 99% LR Protocol: HSA mice received 1 or 4 doses of PGN-EDODM1, with 4-week intervals between doses. Skeletal muscle tissues were collected 4 weeks post-final dose. Skeletal muscle tissue concentration was measured by fluorescent based HPLC method. Graph is presented as mean ± SD; n = 8-12 per cohort. Mis-splicing analysis considers multiple transcripts. Graph is presented as mean ± SD; n = 8-12 per cohort 11 per transcript. Action myotonia evaluation (pinch test) was performed 4 weeks post-final dose. Grade 3 = Clear sign of myotonia strong AND reproducible, Grade 2 = Clear sign of myotonia, strong OR reproducible, Grade 1 = Clear sign of myotonia but non reproducible, Grade 0 = No sign of myotonia. Graphs are presented as mean ± SD; n = 12-43 per cohort.

PGN-EDODM1 – FREEDOM SAD Trial in DM1

Biopsy Biopsy Biopsy Biopsy Biopsy Biopsy Biopsy Biopsy Biopsy FREEDOM SAD FREEDOM: Phase 1 PGN-EDODM1 Single-Ascending Dose Study Design Single Dose PGN-EDODM1 or Placebo (randomized 3:1) Baseline DSMB D28 Wk 16 15 mg/kg FREEDOM Phase 1 n=8 or PBO Study Overview Multinational, randomized, double-blind, placebo-controlled Baseline DSMB D28 Wk 16 SAD study in patients 10 mg/kg n=8 or PBO Single IV administration of PGN-EDODM1 Muscle biopsies in tibialis anterior Baseline DSMB D28 Wk 16 at Baseline, Day 28, Week 16 5 mg/kg n=8 or PBO Safety, PK, correction of mis- splicing, initial functional assessments PGN-EDODM1 dose 13 DSMB: data safety monitoring board; IV: intravenous; PBO: placebo; SAD: single-ascending dose; PK: pharmacokinetics Dosed

FREEDOM SAD PGN-EDODM1 Produced Dose-Dependent Best-in-Class Splicing Correction Following Single Dose * Splicing Index Changes: 22-Gene Panel at D28 3.3% 87.5% of participants across all doses -12.3% showed improved splicing -29.1% -53.7% 1 2 3 Placebo 5 mg/kg 10 mg/kg 15 mg/kg (n=5) (n=6) (n=4) (n=6) 1.Missing samples due to unavailability of biopsy tissue or sample outside of assay window. 2. One subject at 10 mg/kg biopsy was not collected at day 28 due to pseudoaneurysm in connection with biopsy and one participant’s splicing index fell below the pre-specified assay range at baseline and at day 28 (indicating no detectable mis-splicing) 14 3.One subject at 15mg/kg received 77% of the dose and was still included in the splicing index change analysis for the cohort *Provenzano et al., The Splice Index as a prognostic biomarker of strength and function in myotonic dystrophy type 1,J Clin. Invest. 2025 Improvement % Mean change from baseline

Natural History ~11% of Untreated DM1 Patients Demonstrate >20% Splicing Improvement over a 2 to 3 Month Time Period Natural History Data in Untreated DM1 Patients* ~15% OF UNTREATED PATIENTS ~74% OF UNTREATED PATIENTS ~11% OF UNTREATED PATIENTS >20% ±20% >20% Worse Splicing Midrange Correction Splicing Worsens (% Change from Baseline) Splicing Improves (% Change from Baseline) Worsening Improvement +70% +50% +20% 0% −20% −50% −70% Majority Few > +70% of untreated patients demonstrate untreated patients OUTLIER occurs in demonstrate ±20% splicing change <2.6% of cases >20% splicing change from baseline in natural history from baseline over 2-3 months over 2-3 months *Data from C Thornton et al., Lancet Neurology 2023; 22: 218–28. Supplement 15

FREEDOM SAD PGN-EDODM1 Demonstrated >20% Splicing Correction in a Majority of DM1 Patients after a Single Dose ≥10 mg/kg ±20% >20% Splicing Midrange Correction 74% of Untreated Patients Splicing Improves (% Change from Baseline) Improvement Worsening +20% 0% −20% −50% −70% Placebo SAD: 5 mg/kg SAD: 10 mg/kg SAD: 15 mg/kg SAD: 20% Pts >20% 17% Pts >20% 50% Pts >20% 83% Pts >20% +3.3% -12.3% -29.1% -53.7% Mean Splicing Mean Splicing Mean Splicing Mean Splicing N=5 N=6 N=4 N=6 16

FREEDOM SAD Robust, Greater Than Dose-Proportional Increase in Muscle Tissue Concentration Following Single Dose Muscle Tissue Concentration at D28 Mean TA muscle 300 Mean TA Muscle 160.6 160.6 200 100 44.1 44.1 13.7 13.7 0 1,2 1 5 mg/kg 15 mg/kg 10 mg/kg 5mg/kg 10mg/kg 15mg/kg * (n=6) (n=5) (n=5) 1.Missing samples due to unavailability of biopsy tissue 17 2.One subject at 15mg/kg received 77% of the dose and was still included in the muscle tissue concentration analysis for the cohort Concentration (ng/g) Concentration (ng/g) Mean ± SE

FREEDOM SAD PGN-EDODM1 Was Generally Well Tolerated, with TEAEs Primarily Mild to Moderate Across Dose Cohorts • Most frequent TEAEs: nausea, nasopharyngitis, Placebo Cohort 1 Cohort 2 Cohort 3 Total and headache (n=6) 5 mg/kg 10 mg/kg 15 mg/kg (n=24) N (events) (n=6) (n=6) (n=6) • No electrolyte-related TEAEs or hypomagnesemia observed across dose cohorts Any TEAE, n (events) 5 (16) 3 (20) 4 (16) 5 (18) 17 ( 70) • No renal-related TEAEs observed at 5 and 10 Any TEAE by Max Severity mg/kg; DLT at 15 mg/kg involving a transient Mild/Moderate 5 2 2 5 14 decrease in eGFR(cys), resolving without Severe 0 1 2 0 3 intervention Any related TEAE, n • Transient moderate albuminuria observed at 15 1 (3) 1 (1) 2 (4) 4 (14) 8 ( 22) (events) mg/kg and mild albuminuria at 10 mg/kg; Normalized within 2-7 days without intervention Any SAE (event) 1(2) 1 (1) 2 (2) 0 (0) 4 (5) • One drug-related hypersensitivity reaction (rash) Any related SAE 0 0 1 (1) 0 1(1) during infusion at 15 mg/kg, resolving within 2 hours with oral antihistamines Any TEAE leading to study 0 0 0 0 0 withdrawal • One drug-related SAE of severe abdominal pain at 10 mg/kg, confounded by off-label medication Any TEAE leading to death 0 0 0 0 0 use on the day of dosing *As of database lock on December 23, 2025. Unblinded FREEDOM safety data 18 TEAE: treatment-emergent adverse event, SAE: serious adverse event, DLT: Dose limiting toxicity, eGFR(cys): estimated glomerular filtration rate (cystatin equation)

PGN-EDODM1 – FREEDOM2 MAD Trial in DM1

Safety FU Biopsy Safety FU Biopsy Safety FU Biopsy Biopsy Biopsy Biopsy FREEDOM2 MAD FREEDOM2: Phase 2 MAD Study Design 4 Doses of PGN-EDODM1 or Placebo (randomized 3:1) DSMB * FREEDOM2 Phase 2 12.5 mg/kg n=8 or PBO Study Overview Multinational, randomized, double- 7d post final dose blind, placebo-controlled, MAD study open in Canada, UK, NZ, Australia and DSMB South Korea** 10 mg/kg Fully n=8 Enrolled or PBO IV administration of PGN-EDODM1 or placebo every 4 7d post final dose weeks for a period of 12 weeks DSMB Key endpoints: Safety, PK, correction of splicing, functional assessments: vHOT, 5 mg/kg n=8 Complete hand grip, 10-meter walk run test or PBO PGN-EDODM1 dose 7d post final dose FREEDOM-OLE open for patients in FREEDOM & FREEDOM2 DSMB: data safety monitoring board; FU: follow-up; IV: intravenous; MAD: multiple-ascending dose; PBO: placebo; PK: pharmacokinetics; vHOT: video hand opening test; OLE: open label extension 20 * Dose dependent on recommendations of DSMB **The U.S. FDA recently placed a partial clinical hold on FREEDOM2-DM1

FREEDOM2 MAD Favorable Emerging Safety Profile of PGN-EDODM1; No Increase in Toxicity with Multiple Doses at 5 mg/kg PGN-EDODM1 was Generally Well-Tolerated, Summary of Treatment Emergent 5 mg/kg (n=8) 1 with All AEs Mild or Moderate in Severity 1 Adverse Events (TEAEs) n(%) • All participants completed all 4 doses, with no Any TEAE 7 (87.5) evidence of cumulative AEs • The overall AE profile of MAD 5 mg/kg is consistent Mild 4 (50.0) with that observed in SAD 5 mg/kg Moderate 3 (37.5) Severe • Nausea was the most common AE 0 (0.0) • No SAEs, AESIs, or DLTs and no signs of Any SAE 0 hypersensitivity Any related SAE 0 • eGFR and creatinine measurements within the normal range Any AESI or dose-limiting toxicities 0 • No hypomagnesemia Any TEAE leading to study withdrawal 0 • Transient albuminuria observed – did not increase Any TEAE leading to death 0 with repeat dosing 1. Data cutoff date: 04 March 2026 AE: Adverse event; AESI: Adverse event of special interest; DLT: Dose limiting toxicities; SAE: Serious adverse event; TEAE: Treatment emergent adverse event; eGFR: 21 estimated Glomerular Filtration Rate

FREEDOM2 MAD FREEDOM2 5 mg/kg Splicing Correction 5 mg/kg Collective Splicing Data 5 mg/kg Individual Splicing Data FREEDOM2 5mg/kg Mean splicing data Splicing Analysis FREEDOM2- 5mg/kg Individual Splicing data 20 Excluding 100 80 70.8 notable splicing outlier 10 60 mean splicing correction of 0 40 22.9% (n=5) 13.5 20 -10 0 -0.1 -3.1 -20 -20 -16.2 -27.2 -40 -7.3 -7.3 -39.1 -30 -6.8 -60 -55.8 High mean muscle tissue -40 -80 Placebo 5mg/kg Wk13 Pbo2 Pbo1 P1 P3 P4 P6 P5 P2 concentration of PGN-EDODM1 n=2 n=6 of 158 ng/g at Day 7 post-dose (n=5)* Data cutoff date: 04 March 2026 22 *One patient’s muscle tissue concentration reading was pending at cutoff date. Improvement Splice index (Mean % change from baseline ± SE) Improvement Splice index % change from baseline)

FREEDOM2 MAD FREEDOM2 5 mg/kg Myotonia (vHOT): PGN-EDODM1 Shows Promising Middle Finger vHOT Trends at Lowest Dose vHOT Analysis 6 +2.5s 4 (52% CFB) • Excluding notable splicing outlier, the active group 2 remained below baseline (n=5) 0 • Splicing outlier demonstrated -2 22 sec difference between -2.95s nadir and week 16 (23% CFB) -4 -6 BL W4 W8 W12 W13 W16 Placebo 5 mg/kg (n=6) CFB: Change from baseline; SE: Standard error 23 Data cutoff date: 04 March 2026 Improvement

FREEDOM SAD FREEDOM2 MAD FREEDOM2 MAD at 10 & 12.5 mg/kg has Potential to Build Upon Robust Single-Dose Splicing Correction ±20% >20% Splicing Midrange Correction 74% of Untreated Patients Splicing Improves (% Change from Baseline) Improvement Worsening +20% 0% −20% −50% −70% Placebo SAD 5 mg/kg SAD 15 mg/kg SAD 10 mg/kg SAD Placebo MAD: 5 mg/kg MAD: 5 mg/kg MAD: Future Data Readouts: -6.8% -7.3% -22.9% FREEDOM2 MAD Mean Splicing Mean Splicing Mean Splicing N=2 N=6 N=5 at 10 & 12.5 mg/kg without outlier 24

FREEDOM2 MAD Promising Safety, Splicing and vHOT Data in FREEDOM2 Lowest Dose – Supports Ongoing 10 mg/kg MAD Cohort • PGN-EDODM1 was generally well-tolerated; all AEs were mild or SAFETY & moderate in severity, with no SAEs or cumulative toxicity with repeat TOLERABILITY dosing observed • Mean splicing correction of 7.3% with PGN-EDODM1 (n=6) vs 6.8% SPLICING & placebo (n=2) FUNCTIONAL • Analysis excluding one notable splicing outlier demonstrated mean DATA: splicing correction of 22.9% (n=5)​ • Promising trends observed in vHOT in PGN-EDODM1 treated group Company on track to report clinical data from 10 mg/kg multiple dose cohort in 2H 2026 Data cutoff date: 04 March 2026 25 AE: Adverse event; SAE: Serious adverse event

Summary of PGN-EDODM1 and FREEDOM Program 1 Differentiated Delivery Technology PHASE 2 FREEDOM2 MAD & OLE Differentiated Target 2 Promising Safety, Splicing and vHOT Data in FREEDOM2 Lowest Dose – Supports Ongoing 10 mg/kg MAD Cohort FREEDOM STUDY: • Company has completed enrollment in the 10 mg/kg MAD cohort of FREEDOM2 • 13 patients have enrolled in the FREEDOM-OLE at 5 mg/kg, PRIMARY: SAFETY including 6 patients from FREEDOM2 q Favorable emerging safety profile GUIDANCE: • 2H 2026: FREEDOM2 10 mg/kg clinical results EXPLORATORY: PD (SPLICING) • 2027: FREEDOM2 12.5 mg/kg clinical results q Unprecedented splicing correction achieved with single dose Strong cash runway into 2H 2027, through FREEDOM2 12.5 mg/kg MAD readout 26

Thank you