FORTE BIOSCIENCES

Feb 19, 2020 — Tocagen and Forte undertake no obligation to publicly update any timing of the availability of data from Forte’s clinical trials;

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2Certain statements contained in this presentation regarding matte rs that are not historical facts, are forward-looking statemen ts within the meaning of Section 21E of the Securities and Exchange Act of 1934, as amended, and the Private Securities Liti gation Act of 1995, known as the PSLRA. These include stateme nts regarding management™s intention, plans, beliefs, expectations or forecasts for the future, and, therefore, you are cautioned not to place undue reliance on them. No forward-lo oking statement can be guaranteed, and actual results may differ materially from those projected. Tocagenand Forte undertake no obligation to publicly update any forward-looking statem ent, whether as a result of new information, future events or otherwise, except to the extent required by law. We use words such as fianticipates,fl fibelieves,fl fiplans,fl fiexpects,fl fiprojects ,fl fiintends,fl fimay,fl fiwill,fl fishould,fl ficould,fl fiestimates,fl fipredicts,fl fipotential,fl ficontinue ,fl figuidance,fl and similar expressions to identi fy these forward-lookin g statements that are intended to be covered by th e safe-harbor provisions of the PSLRA.Such forward-looking statements are based on our expectations and involve risks and uncertainties ; consequently, actual results may differ materially from thos e expressed or implied in the statements due to a number of factors, includ ing, but not limited to, risks relation to the completion of the transaction, incl uding the need for Tocagenstockholder approval and the satisfaction of closing conditio ns; the anticipated financing to be completed concurrently with the closing of the transaction ;the cash balance of the comp any following the closing the transaction and the financing, and the expectation with respect thereto; the business and prospe cts of the company following th etransaction; and the ability of Tocagento remain listed on the Nasdaq Capital Market. Risks and uncerta inties related to Forte that may cause ac tual results to differ materially from th ose expressed or implied in any forward-looking statement include, but are not limited to: Forte™s pl ans to develop and potentially commercializ e its product candidates, including FB-40 1; the timing of initiation of Fo rte™s planned clinical trials; the timing of the availability of data from Fo rte™s clinical trials; the timing of any pl anned investigational new drug application or new drug application; Forte™ s plans to research, develop and commercialize its current and future produc t candidates; Forte™s ability to successfully enter into collaborations, and to fulf ill its obligations under any such collaboration agreements; the clinical utility, potential benefits and ma rket acceptance of Forte™s product candid ates; Forte™s commercialization, marketing and manufacturing capabilities an d strategy; Forte™s ability to identify additional products or product candidates with significant commercial potential; developments and projections relating to Forte™s competitors and ou r its industry; the impact of government laws and regulations; Forte™s ability to protect its intellectual property position; and Forte™s estimates regarding future revenue, expenses, capital requirements and need for additional financing following the proposed transaction. These risks, as well as other risks associat ed with the transaction, will be fully d iscussed in the proxy statement/prospectus that will be included in the regist ration statement that will be filed by Tocagenwith the SEC in connection with the proposed transactio n. Additional risks and uncerta inties are identified and disc ussed inthe fiRisk Factorsfl section of Tocagen™sAnnual Report on Form 10-K, Quarterly Reports on Form 10-Q and other documents filed from time to time with the SEC. Forward-looking statements included in this presentation are based on information available to Tocagenand Forte as of the date of this presentation. Neither Tocagennor Forte undertakes any obligat ion to such forward-looking statements to reflect events or circumstances after the date of this presentation. CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

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ADDITIONAL INFORMATION AND WHERE YOU CAN FIND IT 3Additional Information About the Proposed Transaction and Where to Find it This communication is being made in respect of a proposed transaction involving Forte Bi osciences, Inc. and Tocagen, Inc. Toc agenintends to file a registrati on statement on Form S-4 with the U.S. Securities and Exchange Commission (t he fiSECfl), which will contain a proxy stat ement/prospectus and other relevant mat erials, and plans to file wi th the SEC other documents regarding the proposed transaction. The fi nal proxy statement/prospectus will be sent to the stockh olders of Tocagenin connect ion with the Tocagenspecial meeting of stockholders to be held to vote on matters relating to the proposed transaction. The proxy statement/prospectus w ill contain information about To cagen, Forte, the proposed transaction, and related matters. STOCKHOLDERS ARE URGED TO READ THE PROXY STATEMENT/PROSPECTUS (I NCLUDING ANY AMENDMENTS OR SUPPLEMENTS THERETO) AND OTHER DOCU MENTS FILED WITH THE SEC CAREFULLY IN THEIR ENTIRE TY WHEN THEY BECOME AVAILABLE, AS THEY WILL CONTAIN IMPORTANT INFORMATION THAT STOC KHOLDERS OF TOCAGEN SHOULD CONSIDER BEFORE MAKING A DE CISION ABOUT THE PROPOSED TRANSACTION AND RE LATED MATTERS. In a ddition to receiving the proxy statement/prospectus and proxy card by mail, Tocagen stockholders will also be able to obtain the proxy statement/prospectus, as well as other fillings cont aining information about Tocagen, without charge, from the SEC™s website ( http://www.sec.gov) or, without charge, on Tocagen™swebsite at https://tocagen.com , by contacting Mark Foletta by phone at (858) 412- 8499, or by electronic mail at [email protected] .No Offer or Solicitation This communication is not intended to and does not constitute an offer to sell or the solicitation of an offer to subscribe for or buy or an invitation to purch ase or subscribe for any securities or the solicitation of any vote or approval in any jurisdiction in connection with th e proposed transaction or otherwise, norsh all there be any sale. Issuance or transfer of se curities in any jurisdiction in contravention of applicable law. No offer of se curities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.Participants in Solicitation Tocagenand its executive officers and directors may be deemed to be participants in the solicitat ion of proxies from Tocagen™ s tockholders with respect to the matters relating to the proposed transaction. Forte may also be deemed a participant in such solicitation. Information re garding Tocagen™ executive o fficers and directors is available in Tocagen™sproxy statement on Schedule 14A for its 2018 Annual Meeting of stockholders, filed with the SEC on April 19, 2019. Information regarding anyin terest that Tocagen, Forte or any of the executive officers or directors of Tocagenor Forte may have in th e transaction with Forte will be set forth in the proxy statement/prospectus that T ocagenintends to file with th e SEC in connection with its stockholder vote on matters relating to th e proposed transaction. Tocagenstockholder s will be able to ob tain this information by reading the proxy statement/prospectus when it becomes available.

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FORTE BIOSCIENCES ŒTOCAGENMERGER 4Forte Biosciences and Tocagen agreed to merge on February 19, 2020 in an all-stock transaction and is expected to trade on Nasdaq under new symbol FBRX The transaction is expected to close in 2Q20Forte Biosciences investors will provide a concurrent financing of $14 million Forte Biosciences holders will own approximately 74.5% and Tocagen holders will own 25.5 %of the combined company, subject to certain adjustments The total cash balance of the combined company is expected to be approximately $25 million Post-Merger Board of Directors to include 8 representation s: 6 designated by Forte Biosciences and 2 designated from Tocagen The transaction has been approved by the Board of Directors of both companies and is subject to stockholder approval of Tocagenholders +

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SUMMARY OF FORTE BIOSCIENCES: FB-401 ŒPOTENTIAL FIRST-IN-CLASS TOPICAL LIVE BIOTHERAPEUTIC FOR THE TREATMENT OF INFLAMMATORY SKIN DISEASE 5LATE-STAGE CLINICAL ASSET Phase 2a trial in atopic dermatitis completed includin g pediatrics 3 years and older, demonstrating safety and efficacy of FB-401. RandomizedPhase 2 initiation in adults and pediatrics 2 years and older expected in mid-2020 in atopic dermatitis (AD) with expected data readout in mid-2021 10-20% of children in industrialized countries develop atopic dermatitis (AD) In the U.S. , AD affects 17 million people (over 50% are children) Significant unmet need for safe and effective AD therapy for pediatrics LARGE MARKET WITH UNMET NEEDClinical data demonstrates safety and activity of FB-401 Phase 2a study, including pediatrics, demonstrates clea n safety profile and significant reduction in atopic dermatitis disease and pruritus, as well as control of S. aureus while tapering/eliminating steroid use POTENTIAL FIRST- IN-CLASS TOPICAL LIVE BIOTHERAPEUTIC Exclusive license to NIH-owned patent families as well as Forte owned IP. Coverage includes composition and method of use patents Patent coverage through at least 2037 (4 U.S. patents issued) INTELLECTUAL PROPERTY Series A financing of $10 million in 2019 from ArrowM arkPartners; concurrent financing of $14 million from experienced life science investors incl uding Alger, BVF Partners LP and OrbiMed Cash runway expected to be sufficient through Phase 2 data readout in mid-2021 Management team with significant drug developmen t, innovation and corporate strategy experience FINANCING / MANAGEMENT

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FORTE BIOSCIENCES: OVERVIEW OF FB-401 6FB-401 drug product consists of 3 therapeutic bacterial strains of commensal gram negative R. mucosa specifically selected based on screening for impact on inflammatory skin disease parametersTopical application of the specifically selected therapeutic bacterial strains of R. mucosa drug product: Drives immune pathways that are defective Suppresses Staphylococcus aureus growth Improves skin barrier function Clinical data demonstrates safety and activity of FB -401 live biotherapeutic therapy in both adults and pediatricPhase 2a study, including pediatrics, demonstrates clea n safety profile and significant reduction in atopic dermatitis disease and pruritus, as well as control of S. aureus while tapering/eliminating steroid use RandomizedPhase 2 trial initiation expected in mid-2020

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ATOPIC DERMATITIS Atopic dermatitis (AD) is characterized by itching, a scal y rash, dry skin, and cutaneous sensitization to allergens. The underlying pathology of AD consists of a triad of defective skin barrier function, susceptibility to Staphylococcus aureusskin infection, and immune imbalance (overactive adaptive immunity in lieu of innate immunity) 10-20% of children in industrialized countries develop atop ic dermatitis with increasing incidence. 80% of children with severe disease continue to have lifelong exacerbations There is currently no cure for AD In the US, the prevalence of atopic dermatitis is approximately 17 million More than half of that prevalence is pediatric (<17 years old) Treatment options for pediatrics are very limited FDA Pediatric Subcommittee October 29-30, 2003 American Academy of Dermatology Affects flexural areas of neck, elbows, knees, wrists, and anklesLichenified, erythematous plaques behind the kneesErythematous, excoriated papules with overlying crust in the antecubital fossa Erythematous ill- defined patches with overlying scale and erosions on her cheeks8 PAGE - 9 ============ SKIN MICROBIOME Drenoet al, European Academy of Dermatology and Venerology 2016, 30, 2038-2047 Kong HH et al. Genome research. 2012;22(5):850-859 The skin is a complex barrier organ charac terized by symbiotic relationship between microbial communities and host tissue via comp lex signals provided by the innate and the adaptive immune systems Exposure to various endogenous and exogeno us factors impact the system balance potentially leading to inflammatory skin cond itions comprising infections, allergies or autoimmune diseases Researchers in microbiology and dermato logy identified and characterized the microorganisms present on the skin, to evaluate the bacterial diversity and their relative abundance and to understand how microbial di versity may contribute to skin health and dermatological conditions Recent work has revealed that the skin micr obiome is significantly different between healthy controls and patients with AD and th at symptoms are associated with a loss of commensal diversity 9 PAGE - 10 ============ SKIN MICROBIOME DIFFERENCES IN ATOPIC DERMATITIS Myles IA, Williams KW, ReckhowJD, et al. JCI Insight. 2016;1(10) Kong HH et al. Genome research. 2012;22(5):850-859 Genetic-based microbiome identification revealed significant differences in the Gram-negative skin biome between atopic dermatitis (AD) patients and healthy controls (HV) NIH (Myles et. al.) identified substantial differences in the gram-negative microbiome present on the skin of AD patients and healthy volunteers The predominant species of skin commensal Gram-negative bacteria (CGN) in HV found to be Roseomonasmucosa Over 50% of AD patients did not have any culturable Gram- negative flora, consistent with DNA-based analysis 10 PAGE - 11 ============ PHASE 2A FIRST HUMAN STUDY OF FB-401 -CUTANEOUS LIVE BIOTHERAPEUTIC FOR THE TREATMENT OF ATOPIC DERMATITIS Drug product: FB-401 (3 specifically selected therapeu tic R. mucosa strains) lyophilized and reconstituted with sterile water in single-use, self-administered spray Design: Phase 1/2a enrolled 2 cohorts: Initial cohort enrolled 10 adult atopic dermatitis patients 18 years and older Following positive safety assessment from coho rt I, the second cohort of 20 pediatric patients was enrolled Primary Objective: To evaluate the safety and activity of R mucosa as a live biotherapeutic for treatment of AD Secondary Objective: To evaluate the effect of R mucosa live biotherapy on quality of life of participants with AD Exploratory ObjectivesMeasure trans epidermal water loss (TEWL) Characterize changes to total and specific IgE Evaluate potential changes to pre-diagnosed asthma and/or food allergies Evaluate incidence of S aureus infections that require treatment Persistence of R mucosa colonization after treatment 11 36 KB – 19 Pages