Disclosures For the purposes of this notice, the "presentation" that follows shall mean and include the slides that follow, the oral presentation of the slides by members of management of Selecta Biosciences, Inc. ("Sele

Disclosures For the purposes of this

notice, the "presentation" that follows shall mean and include the slides that follow, the oral presentation of the slides by members of management of Selecta Biosciences, Inc. ("Selecta") and Cartesian Therapeutics, Inc.

("Cartesian") or any person on their behalf, any question-and-answer session that follows such oral presentation, hard copies of this document and any materials distributed at, or in connection with, such oral presentation. No

Representations and Warranties This presentation is being distributed solely to qualified institutional buyers and accredited investors with sufficient knowledge and experience in investment, financial and business matters and the capacity to

conduct their own due diligence investigation and evaluation. This presentation is for informational purposes only and to assist such parties in making their own evaluation with respect to the potential combination (the "Proposed

Merger") of Cartesian with and into a wholly-owned subsidiary of Selecta and related transactions and not for any other purpose. This presentation does not purport to contain all of the information that may be required to evaluate a possible

investment decision with respect to the Proposed Merger and related transactions. The recipient agrees and acknowledges that this presentation is not intended to form the basis of any investment decision by the recipient and does not constitute

investment, tax or legal advice. No representation or warranty, express or implied, is or will be given by Selecta or Cartesian or any of their respective affiliates, directors, officers, employees or advisors or any other person as to the accuracy

or completeness of the information in this presentation or any other written, oral or other communications transmitted or otherwise made available to any party in the course of its evaluation of a possible transaction between Selecta and Cartesian.

Forward-looking Statements Any statements in this presentation about the future expectations, plans and prospects of Selecta and/or Cartesian, including without limitation, statements regarding the Proposed Merger, expectations regarding the timing

and perceived benefits of the Proposed Merger, the proposed concurrent financing (the "Financing"), expectations regarding the use of proceeds from the Financing, expectations regarding the timing and outcome of the special stockholder

meeting to be held following the Proposed Merger, including the likelihood that stockholders will approve the conversion of preferred stock issued in the Proposed Merger and the Financing into common stock, Selecta's and Cartesian's

ability to efficiently integrate operations following the Proposed Merger, the combined company's cash runway, the combined company's ability to execute its development plans and manage its operating expenses, the unique proprietary

technology platform of Selecta, Cartesian or the combined company, expectations regarding the safety and efficacy of Cartesian's Descartes-08 product candidate, RNA Armory proprietary platform and other pipeline candidates, the anticipated

timing or the outcome of ongoing and planned clinical trials, studies and data readouts, the anticipated timing or the outcome of the FDA's review of the combined company's regulatory filings, the combined company's and its

partners' ability to conduct its and their clinical trials and preclinical studies, the timing or making of any regulatory filings, the anticipated timing or outcome of selection of developmental product candidates, the potential treatment

applications of the combined company's product candidates, the novelty of treatment paradigms that the combined company is able to develop, whether the observations made in non-human study subjects will translate to studies performed with

human beings, the potential of any therapies developed by the combined company to fulfill unmet medical needs, and other statements containing the words "anticipate," "believe," "continue," "could,"

"estimate," "expect," "hypothesize," "intend," "may," "plan," "potential," "predict," "project," "should," "target,"

"would," and similar expressions, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Actual results may differ materially from those indicated by such forward-looking

statements as a result of various important factors, including, but not limited to, the following: the uncertainties related to the timing and expected benefits of the Proposed Merger, the uncertainty inherent in the outcome of stockholder votes at

the special stockholder meeting to be held in connection with the Proposed Merger, the uncertainties inherent in the initiation, completion and cost of clinical trials including proof of concept trials, including the uncertain outcomes, the

availability and timing of data from ongoing and future clinical trials and the results of such trials, whether preliminary results from a particular clinical trial will be predictive of the final results of that trial and whether results of early

clinical trials will be indicative of the results of later clinical trials, the ability to predict results of studies performed on human beings based on results of studies performed on non-human subjects, the unproven approach of the combined

company's technology, potential delays in enrollment of patients, undesirable side effects of the combined company's product candidates, its reliance on third parties to conduct its clinical trials, the combined company's inability

to maintain its existing or future collaborations, licenses or contractual relationships, its inability to protect its proprietary technology and intellectual property, potential delays in regulatory approvals, the availability of funding sufficient

for its foreseeable and unforeseeable operating expenses and capital expenditure requirements, recurring losses from operations and negative cash flows, substantial fluctuation in the price of the combined company's common stock, risks related

to geopolitical conflicts and pandemics and other important factors discussed in the "Risk Factors" section of the Selecta's most recent Annual Report on Form 10-K and subsequently filed Quarterly Reports on Form 10-Q, and in other

filings that the Selecta makes with the Securities and Exchange Commission (the "SEC"). In addition, any forward-looking statements included in this presentation represent Selecta's and Cartesian's views only as of the date

of its publication and should not be relied upon as representing its views as of any subsequent date. Each of Selecta and Cartesian specifically disclaims any intention to update any forward-looking statements included in this presentation, except

as required by law. Disclaimers and Forward-Looking Statements

No Offer or Solicitation; Important

Information About the Proposed Merger and Where to Find It This presentation is not a proxy statement or solicitation of a proxy, consent or authorization with respect to any securities or in respect of the Proposed Merger and shall not constitute

an offer to sell or a solicitation of an offer to buy the securities of Selecta or Cartesian, nor shall there be any sale of any such securities in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to

registration or qualification under the securities laws of such state or jurisdiction. No offer of securities shall be made, except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended, or an

exemption therefrom. The combined company expects to file a proxy statement with the SEC relating to the proposals to be voted upon at an upcoming meeting of stockholders (the "Meeting Proposals"). The definitive proxy statement will be

sent to all combined company stockholders. Before making any voting decision, investors and security holders of the combined company are urged to read the proxy statement and all other relevant documents filed or that will be filed with the SEC in

connection with the Meeting Proposals as they become available because they will contain important information about the merger agreement and the related transactions and the Meeting Proposals to be voted upon. Investors and security holders will be

able to obtain free copies of the proxy statement and all other relevant documents filed or that will be filed with the SEC by the combined company through the website maintained by the SEC at www.sec.gov. Participants in Solicitation Selecta,

Cartesian, and their respective directors, executive officers and employees may be deemed to be participants in the solicitation of proxies in respect of the Proposed Merger. Information regarding Selecta's directors and executive officers is

available in the Selecta's Annual Report on Form 10-K for the year ended December 31, 2022 filed with the SEC on March 2, 2023. Information regarding the persons who may, under the rules of the SEC, be deemed participants in the proxy

solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the proxy statement and other relevant materials to be filed with the SEC when they become available. Disclaimers and

Forward-Looking Statements

Selecta and Cartesian merger to create

publicly traded company pioneering RNA cell therapy to treat autoimmune disease Pro forma cash resources expected to fund continued clinical development of Descartes-08 through Phase 3 and multiple additional clinical programs Cartesian Opportunity

Leader in RNA cell therapy with approach to treating autoimmune disease Deep pipeline of autoimmune programs Strong IP portfolio Clinically Validated Lead Program Descartes-08: observed deep and durable clinical responses in myasthenia gravis (MG)

patients in Phase 2a study Integrated Capabilities Merger to create fully integrated organization with in-house cGMP manufacturing, R&D, regulatory, clinical operations, and existing public company infrastructure Near-Term Catalysts Plan to

initiate Phase 2 trial for Descartes-08 in SLE in 1H 2024 Phase 2b data for Descartes-08 in MG expected in mid-2024 Plan to initiate Descartes-08 ocular autoimmune basket trial in mid-2024 Plan to initiate Descartes-08 vasculitic autoimmune basket

Planning to announce sign and close of

Selecta/Cartesian stock for stock Merger on or about Nov 13, 2023 Selecta to issue < 20% of voting common stock plus non-voting convertible securities as consideration Conversion of convertible securities to be subject to stockholder vote

post-close Relative ownership split pre-PIPE is expected to be approximately 73% and 27% Cartesian and Selecta stockholders, respectively Deal Overview Selecta stockholders to receive: Proportionate ownership in merged company CVR to receive future

economic benefits related to legacy Selecta assets, net of certain Selecta liabilities PIPE to be announced concurrently with deal announcement Anchored by Board member of Selecta, Tim Springer PIPE investment is in, and use of proceeds is to fund,

Cartesian pipeline Expected pro forma cash of over $100 million

Cartesian - Clinical-stage

company pioneering RNA cell therapy for autoimmunity Expanding the Reach and Potential of Cell Therapy RNA cell therapies do not require lymphodepletion Designed to be dosed more reliably and repeatedly at safe therapeutic doses versus DNA analogs

Promising Lead Asset Descartes-08, a potential first-in-class RNA CAR T-cell (rCAR-T) therapy for autoimmune diseases Successful Phase 2a trial using an engineered cell therapy to treat autoimmunity In-House Manufacturing and R&D Wholly-owned,

state-of-the-art GMP manufacturing Designed to optimize processes rapidly and iteratively Robust Pipeline Based on Proprietary Platform RNA Armory designed to enable precision control and optimization of engineered cells for diverse cell

therapies Modalities include autologous, allogeneic, and in vivo transfection approaches

Combined organization overview Matthew

Bartholomae General Counsel Metin Kurtoglu, MD, PhD COO Milos Miljkovic, MD CMO Blaine Davis CFO Chris Jewell, PhD Chief Scientific Officer Carsten Brunn, PhD President and CEO Murat Kalayoglu, MD, PhD Director Cartesian Co-Founder and pre-merger

CEO Carrie S. Cox Chairman Michael Singer, MD, PhD Director Cartesian Co-Founder and pre-merger Chief Strategy Officer Timothy Springer, PhD Director Management Select Board Members Experienced management team to lead the RNA cell therapy company of

the future Emily English, PhD VP, Quality

Effector function of cell therapy

engineered with DNA amplifies exponentially with cell replication, frequently leading to uncontrollable PK/PD Cells administered at subtherapeutic levels quickly proliferate beyond therapeutic window Conventional engineered cell therapy uses DNA,

which can lead to toxicity and high cost DNA CAR-T cell therapy is expensive Direct costs high due to viral vector manufacturing and release of final product Indirect costs high due to monitoring/treatment of toxicities DNA transduced CAR-T

associated with: Cytokine release syndrome (CRS) Neurotoxicity and parkinsonism Infections Death Cytopenia (from pre-treatment chemo)

Limited experience with DNA CAR-T in

autoimmunity shows significant toxicity that can be incompatible with outpatient treatment DNA CAR-T in neuromyelitis optica1 12 of 12 patients with Grade 3-4 cytopenias 12 of 12 patients with CRS 7 of 12 patients with Grade 3 infections DNA

CAR-T in systemic lupus erythematosus2 5 of 5 patients with Grade 3-4 cytopenias 3 of 5 patients with CRS;1 requiring tociluzimab DNA CAR-T in antisynthetase syndrome3 1 of 1 patient with Grade 3 cytopenia 1 of 1 patient with CRS treated with

tociluzimab 1 of 1 requiring IVIg DNA CAR-T in severe systemic sclerosis4 1 of 1 patient with cytopenia 1 of 1 patient with CRS 1Qin et al Sig Transduction Targeted Ther 2022, 2Mackensen et al Nature Med 2022, 3Muller et al Lancet 2023, 4 Bergmann

Ann Rheum Dis 2023 DNA CAR-T in neuromyelitis optica (Phase 1 study) DNA CAR-T in lupus (compassionate use only)

mRNA does not replicate

predictable half-life with more controllable PK/PD defined by the dose No requirement for cell proliferation no expected need for pre-treatment chemo no Grade 3-4 cytopenias Cartesian's RNA approach designed to expand reach of

cell therapy to autoimmunity with safer, potent, and less expensive therapies Descartes-08 has been administered to 66 patients with autoimmune diseases and cancer1 with no CRS, neurotoxicity, or infections observed Treatment with potential to be

administered in community clinics Expectation for cells to be administered in multiple doses and, if needed, in more than one cycle rCAR-Ts have potential to be less expensive than DNA CAR-Ts Lower manufacturing costs Lower treatment costs since no

expected need for expensive hospitalization, toxicity management, and monitoring Time Therapeutic window Subtherapeutic Toxicity CAR+ Cells 6 Doses 1All open-label patients treated with Descartes-08 as of Oct 30, 2023

Wholly-owned pipeline targets

autoimmune disease AAAD, autoantibody-associated autoimmune diseasesSLE, Systemic Lupus Erythematosus rMSC, Mesenchymal Stem Cells transfected with mRNALN, Lymph node Asset Indications Discovery/ Preclinical Phase 1 Phase 2 Pivotal Descartes-08

Autologous rCAR-T Myasthenia Gravis SLE, other AAAD Descartes-15 Autologous rCAR-T AAAD Descartes-33 Allogeneic rMSC AAAD In vivo LN transfection Undisclosed Data from Phase 2b study expected in mid-2024 Expect to initiate Phase 2 studies in SLE,

ocular and vasculitic autoimmune diseases in 2024 Next-gen anti-BCMA rCAR-T with >10x preclinical potency

In-house manufacturing enhances

control of product quality, production schedules and costs cGMP Cell Manufacturing State-of-the-art facility with dedicated QMS cGMP RNA Synthesis Large-scale RNA production MSC Cell Banking Part 1271, FDA-reviewed huMSC collection & banking

Process Development Processes optimized through >200 cGMP runs Quality Control Internal assay validation and lot release

Initial indication for

Descartes-08: Myasthenia gravis Affects over 120,000 patients in US and EU Characterized by debilitating weakness: limbs, respiratory, ocular, facial muscles Standard of care includes chronic use of immunosuppressants, which are often toxic

Progressive disease that is fatal in 1/3 of patients without immunosuppressants Newer agents include complement inhibitors and anti-FcRn mAbs, which only offer modest responses and must be administered chronically to maintain those responses

Pathogenesis is similar across many autoimmune diseases; involves attack on self by both T cells and B/plasma cells

Descartes-08 is believed to be the

first rCAR-T in clinical development for autoimmune disease Descartes-08 Engineered by transfection of autologous CD8+ T cells with mRNA encoding anti-BCMA CAR Typical lot processed for infusion within ~3 weeks Observed to enhance killing and

suppression of inflammatory cytokine secretion versus T cell therapies derived from pan T cell sources Positive Phase 2a data in myasthenia gravis underscores potential for deep and durable responses versus current agents Granted U.S. FDA orphan

designation for generalized myasthenia gravis (2022)

CAR-T in autoimmunity offers

differentiated, multi-modal mechanism of action FcRn Inhibitors Complement Inhibitors Reduces complement Reduces autoantibody CAR-T Cells Designed to: Reduce target cell populations (BCMA+ or B cells) Reduce plasma cell ligands (Descartes-08 only)

Reduce autoantibody Reduce inflammatory cytokines Induce dramatic shifts in T- and B- cell repertoires Modest responses Goal: Deep, durable responses Conventional Approach CAR-T Cell Therapy

Phase 2 study of Descartes-08 in MG

(NCT04146051) Part 1: Identify safe dose (n = 3) Complete Part 2: Determine optimal dosing schedule (n = 12) Complete1 Part 3: Phase 2b comparing Descartes-08 to placebo (n = 30) Enrolling All doses safe and well-tolerated Six weekly infusions led

to deep, durable responses Placebo-controlled trial for engineered adoptive cell therapy 1 Continues to enroll patients with MuSK MG and subjects who are otherwise not eligible for Part 3 MG-ADL, Myasthenia Gravis Activities of Daily Living

scale MGFA, Myasthenia Gravis Foundation of America Patient eligibility MG-ADL > 6 MGFA Class II-IV Stable medication dosing > 8 wks prior to infusion 4-week washout for biologics IVIg and plasma exchange not allowed after starting

Descartes-08 Patients on immunosuppression or complement inhibitors expected to be able to continue their treatment while receiving Descartes-08 Cell manufacturing platform tolerates most standard immunosuppressive therapies

Phase 2a study population comprises